What do you do when you feel so sick you can't really concentrate let alone sleep?

It’s 12:30am, I have to get up tomorrow today to babysit my cousins but my tummy really really hurts I feel really quite sick and I can hardly do anything. This happened to me the other night too and I couldn’t concentrate enough to finish off my big essay properly that was due the next day and it ended up being a really bad piece of writing but I had no choice but to hand it in like that. Any suggestions?