Sometimes having someone at work who knows what's been going on with you will help a great deal. You don't have to go into details. But you can make up any excuse you like, some people probably won't ask out of fear that it may seem rude to ask. But if they do, they won't mind at all if you don't explain yourself to them.
Just think.. you've been to work before and been fine, so it's a proven fact you are able to do it again. It's just a normal day at work.
I wish you good luck for your first day back, I'm sure you'll do fine.
Buy some rescue remedy too. It's quick and sneaky. Either in a glass of water or the spray. No one will ever know