Is Lucid Dreaming Dangerous?
Although the majority of lucid dream enthusiasts might be quick to say that lucid dreaming is completely safe, I would say that dream work in general is mostly safe. Dreaming, usually composed of challenges and threats, can be disruptive to your waking life. When dreams are particularly disturbing, we call these nightmares, but most dreams are stressful to some degree. Practices intended to increase activation of the dream-generating-system for lucid dream purposes may also increase frightening dream content, sleep paralysis, false awakenings, and maybe, just maybe next-day out-of-sorts. In fact, many lucid dreams are immediately prefaced by super-uncomfortable dream imagery. It's almost as if in these instances we push through the dream threat, and the bravery is rewarded by the clarity of thought we enjoy in lucid dreams.
Looking at the situation from a couple of other angles, studies have shown that the experimental reduction of REM-sleep can reduce symptoms of depression, and it is a definite that anti-depressant drugs greatly reduce REM-sleep and recall of dreaming. But these are special populations, already experiencing mental disturbance.
In persons with healthy-enough minds, paying attention to one's dreams through journaling, and the attempt to dream lucidly are not going to have an adverse on your waking life. I don't recommend that most people record their dreams in a journal every day of their lives. For one thing, with a little practice you begin to remember more and more dream content and just writing or typing your dreams (up to five or sic per night!) can become a real time-strain. And it's tiring. And I do think that paying attention to your dreams over a long while can drain your emotions. I noticed this with my own dream recording, and also when reading dreams from my study participants. So, work with dreams in moderation f it seems to become a chore or make you feel bad. I'm guessing that many people have ignored these affects under the false-belief that dreams are supposed to be fluffy clouds of smiles.