I had pretty much identical problems to yours. I've been using melatonin that way for about 4 or 5 years now, and haven't noticed any real side effects.
* It does make me very thirsty a little bit after taking it; now I just make sure to drink plenty of water along with it. (I normally take pills without water, so I probably noticed this more than most people.)
* I think subjectively I end up sleeping for longer if I don't actually need to get up. But it doesn't prevent me from waking up if it's something important (like work).
I do mostly follow the suggestion to go a week without it every few months.
The only change in its behavior I've noticed is that it no longer gives me the vivid dreams it did for the first couple months.
* It does make me very thirsty a little bit after taking it; now I just make sure to drink plenty of water along with it. (I normally take pills without water, so I probably noticed this more than most people.)
* I think subjectively I end up sleeping for longer if I don't actually need to get up. But it doesn't prevent me from waking up if it's something important (like work).
I do mostly follow the suggestion to go a week without it every few months.
The only change in its behavior I've noticed is that it no longer gives me the vivid dreams it did for the first couple months.