Is it OK for me to resign without giving notice?

I would read over the paperwork you were givin when you were hired just to be sure but if legality is what you are concerned about then i don't think you have anything to worry about. As far as work integrity, you will lose all that you've worked for though. If you are worried about someone being upset, you should just say you have to resign & not worry about it,but if you think your boss will become irrational and your fears are legitimate then either tell a higher authority or just quit if that's what you feel is necessary. Good Luck

If you work without a contract, you certainly can walk away at any time with or without notice. Just realize if you do you can probably not count on a good reference from that company.

You can just walk out,but make sure that you never need them to give you a reference for another job.

that's more effective to provide word. yet on your difficulty i might want to communicate over such as your manager and clarify about the internship. Then do what you want to do. yet leaving without word will maximum in all probability burn bridges.