Just a normal effect if your body is getting used to it. Nothing to
really worry about but it is really annoying. If your fellows are awake until sunrise they should think about stop it for some weeks. Sounds a little creepy.
Cannabis is a drug, some people
forget this. Ha, wordplay.
So regarding seriously to topic: cannabis is probably one of the most healthy medicine to some serious diseases. It is a drug, like alcohol, nicotin, cocaine, heroine, sugar, caffeine, watching tv and a lot of other things, and last but not least: medicine. But it is
way less harmful than public thinks. And, like with any drug, you should only use it for fun if you're psychological and physically stable. And you should not get used to it.