It is not recommended, you could severely damage your eye if your optometrist says so, too. I once slept in my contacts for 4 hours and my eyes were super dry after and I had to get them checked (I ended up fine, but I don't want to have to do that stressful experience again)! So I think it's best to not sleep in them. If anything happens to your contacts, just see if you can get new ones (and a case!), and until then, wear glasses.
It depends on the type you have. Some are made for you to sleep in and some are not. There is also the chance of them getting stuck on your eyelids.
