"All statements regarding Kundalini should always be treated with the greatest reserve, partly because the personal equation of the experimenting individual looms very large - Kundalini acting very different in different cases - and partly because nothing ought to appear in print which might give even the slightest assistance in the development of a power which destroys ruthlessly when it is sought to be awakened before its due time.
[...] Before anyone seeks to arouse Kundalini let him know much about it, especially of its dangers, let him be intimately acquainted with these. [...] A little knowledge may incline him to foolishness.
[...] The path of occultism, it is said, is strewn with wrecks. I venture to think that the path of the arousing of Kundalini, even if only in the first stages, is strewn with even more wrecks.
[...] It becomes apparent that Kundalini may well be compared with electricity as to the uses to which it can be put. Continuous consciousness, remembrance of events during the night, and so on, are only certain fruits of the arousing of Kundalini. Even more important is the directly added power it gives for work in the outer world.
[...] Mercifully, the world is preserved from the discovery by science of the Kundalini Ray, or annihilation would ensue. When we read of so-called "Death Rays" and other highly destructive emanations from great centres of Force, we may think of Kundalini as more powerful than all of them put together, and we shall be glad to leave it alone until it is necessary that we should learn to use it. It turns in boomerang fashion with terrible effect upon those who misuse it, upon those who do not reverence it, upon those who use it to selfish ends."
G. S. Arundale; "Kundalini - An Occult Experience"
"Unless the mind has been disciplined from an early age, a stimulated kundalini brings with it an irrepressible desire for the occult and the bizarre. It is incredible to what extent the victims of this desire can be duped by pseudo-Godmen, charlatans and impostors...In my own lifetime, one of these Godmen, residing in a village in Kashmir, used to urinate into a silver vessel in full view of the crowds that came to visit him and then sprinkled the liquid over the audience, both men and women. It is even said that his admirers held up their faces and uncovered their bosoms to receive the sanctifying drops." ()[...]
"The nights were even more terrible. I could not bear to have a light in my room after I had retired to bed. The moment my head touched the pillow a large tongue of flame sped across the spine into the interior of my head. It appeared as if the stream of living light continuously rushing through the spinal cord into the cranium gathered greater speed and volume during the hours of darkness. Whenever I closed my eyes I found myself looking into a weird circle of light, in which luminous currents swirled and eddied, moving rapidly from side to side. The spectacle was fascinating but awful, invested with a supernatural awe which sometimes chilled the very marrow in my bones." [...]
"Like the pendulum of a clock, it oscillates between hope and fear, anxiety and assurance, joy and sorrow, for no apparent reason, as if pushed from this side to that and back again by an invisible force from within in a manner entirely unpredictable to the subject of the experience. If the will is not firm and lacks the strength to hold itself in check, the oscillations can lead to those irresponsible acts which are a characteristic of mental disorder." [...]
"Whenever my mind turned upon itself I always found myself staring with growing panic into the unearthly radiance that filled my head, swirling and eddying like a fearsome whirlpool; I even found its reflection in the pitch darkness of my room during the slowly dragging hours of the night. Not infrequently it assumed horrible shapes and postures, as if satanic faces were grinning and inhuman forms gesticulating at me in the darkness." [...]
No one could even suspect what was happening to me inside. I knew that but a thin line now separated me from lunacy, and yet I gave no indication of my condition to anyone. I suffered unbearable torture in silence, weeping internally at the sad turn of events, blaming myself bitterly again and again for having delved into the supernatural without first acquiring a fuller knowledge of the subject and providing against the dangers and risks of the path."
"The thirst for bizarre stories is unassuagable. A whole library of books containing the most fantastic and bizarre stories, which no sane mind can believe, cannot extinguish or satisfy the widespread hunger for the irrational and fanciful.
This thirst, which appears inexplicable to a rational mind, is caused by the stimulation of kundalini in an undisciplined system as the first warning to show that the mind is in an unhealthy state. The desire for strange drug experiences, for erratic psychic phenomena, for fantastic messages received from mediums and sensitives, for the strange actions of gurus and occult teachers, springs from this unhealthy condition of the mind. Today, the Western world is in the grip of a mass hysteria which, if not remedied in time, will revive all those grotesque and orgiastic creeds and cults, including witchcraft, which have been a feature of all decadent cultures in the past."
Gopi Krishna; Living With Kundalini
"The raising of the kundalini force - if brought about ignorantly and prematurely -may produce the rapid burning through of the protective web of etheric matter which separates the various areas of the body (controlled by the seven centres) from each other. This causes serious nervous trouble, inflammation of the tissues, spinal disease, and brain trouble."
Alice Bailey & Djwhal Khul - Esoteric Psychology II - Chapter II
".....for meditation is dangerous and unprofitable to the man who enters upon it without the basis of a good character and of clean living. Meditation then becomes only a medium for the bringing in of energies which but serve to stimulate the undesirable aspects of his life, just  as the fertilizing of a garden full of weeds will produce a stupendous crop of them, and so crush out the weak and tiny flowers. Meditation is dangerous where there is wrong motive, such as desire for personal growth and for spiritual powers, for it produces, under these conditions only a strengthening of the shadows in the vale of illusion and brings to full growth the serpent of pride, lurking in the valley of selfish desire. Meditation is dangerous when the desire to serve is lacking. Service is another word for the utilization of soul force for the good of the group. Where this impulse is lacking, energy may pour into the bodies, but - lacking use and finding no outlet - will tend to over-stimulate the centers, and produce conditions disastrous to the neophyte."
Alice Bailey & Djwhal Khul - A Treatise on White Magic
"Dangers to the Physical Brain
The brain suffers principally in two ways:
From congestion, causing a suffusion of the blood  vessels and a consequent strain upon the delicate brain tissue. This may result in permanent injury, and may even cause imbecility. It shows in the initial stages as numbness and fatigue, and if the student persists in meditation when these conditions are sensed the result will be serious. At all times a student should guard against continuing his meditation when any fatigue is felt, and should stop at the first indications of trouble. All these dangers can be guarded against by the use of common sense, and by remembering that the body must ever be trained gradually and be built slowly. In the scheme of the Great Ones, hurry has no place.
From insanity. This evil has often been seen in earnest students who persist in unwise pressure or seek unguardedly to arouse the sacred fire through breathing exercises and similar practices; they pay the price of their rashness through the loss of their reason. The fire does not proceed in due geometrical form, the necessary triangles are not made, and the electrical fluid rushes with ever increasing speed and heat upwards, and literally burns away all or part of the brain tissue, thus bringing about insanity and sometimes death."
Alice Bailey - Letters on Occult Meditation - Letter V
"The applicant who misuses knowledge, who indulges in such practices as 'breathing for development',or concentrating upon the centers, will inevitably fail in his endeavor to reach the portal, and will pay the price in his body by the appearance of insanity, of neurasthenic conditions, and various physical ills."
Alice Bailey - Initiation, Human and Solar - Chapter XIX
"The seeker who dares to awaken the kundalini power without the grace and guidance of a guru might become insane, succumb to diseases, or even die. This is because he does not possess the necessary knowledge, steadiness of mind, or patience required for this difficult undertaking."
Swami Kripalu - Science of Meditation; The Menace of Kundalini during Dharana