Hello!
I hope this is the right place to post this
I was wondering how much sleep is "healthy" during a diet. I read that sleep is mandatory to allow muscle to form after training, but also that metabolism drops if one sleeps too much.
How much is too much though? (And how much is too little?)

I try to get in my 8 hours, any less than 7 I'm a zombie. I guess overall if you are tired then you aren't sleeping enough...

Personally, I run best on about 6.5-7 hours of sleep per night. If I sleep 8 hrs or more, I tend to actually feel more lethargic and tired when I wake up than I do if I sleep about 7 hrs. I think the amount of sleep you need is a very individual, personal thing though that can vary depending on your bodychemistry, lifestyle etc. My dad has gone his entire life sleeping exactly 6 hours per night, waking up at 5:30 am and going to bed shortly after 11pm every single day. My mom, on the other hand, really really needs a full 8 - 8.5 hours of sleep or she struggles. So the advice of "if you feel tired, you probably need more sleep" given above is probably the best advice you can get - just try to pay attention to your energy levels and listen to your body, there isn't an exact number that anyone can give to anyone else.

i think everyone's body is different in terms of sleep requirement. I prefer 7-9, preferably 8 or 9 and it also depends on how i have been sleeping the couple of days before.
i keep reading that the recommended level is anywhere between 6-8

I usually get between 7-8. But I find that I don't sleep as well when I'm dieting. I go to sleep fine but if I wake up around 3 or 4, it is hard to go back to sleep. I sleep better when I'm overeating...