Exact scientific proof that entering lucid dreaming is dangerous – or even safe – does not exist; there has never been an exhaustive, controlled study to prove either supposition. However, since lucid dreaming exists at the fringes of naturally-occurring states of mind, it can hardly be assumed dangerous. Notably, lucid dreaming is accompanied by rapid eye movement (REM), which every human experiences for up to 2 hours each night, and this begins to explain lucid dreaming experience as entirely safe and natural.
Already confirmed are the psychological influences of lucid dreaming on the physical mind and body; namely, the emotional effects that can occur during the onset of lucid dreaming state.
lucid dreaming entry is a very profound, incredible experience that may induce fear, which is invoked by a natural instinct for self-preservation. lucid dreaming can create stress. This is especially true for novices and those poorly acquainted with the nature of the phenomenon and techniques used to control it. Without knowledge and proper practice, a fear-induced reaction can escalate into full-blown terror. After all, while in lucid dreaming, fantasy quickly becomes reality, and reticent fears can take on hyper-realistic qualities. When this occurs, it’s not lucid dreaming environment, but the fear that is treacherous. It goes without saying that fear is a toxic influence, especially to sensitive souls, the elderly, and people with physical ailments, like certain cardiovascular conditions. This does not mean that persons in these groups should abstain from practicing lucid dreaming. The solution is to learn about and avoid common stressors associated with the practice, know the mechanics of controlling objects, and understand the principles of making an emergency exit.
Given the possibility of negative lucid dreaming experiences, it could be advised that practitioners limit the time in lucid dreaming to fifteen minutes, though it is quite exceptional to maintain lucid dreaming for such duration. Proposed time limits are entirely theoretical and motivated by the fact that natural REM does not normally last longer than fifteen minutes, and, at the risk of side effects due to the alteration of natural cycles, experiments directed at unnaturally prolonging REM are not recommended.