I ended up with a stomach ulcer after taking some cheap painkillers some years ago, have avoided them like the plague since.
I was scared silly as to what it was and due to the symptoms remember sat in the loos in Morrisons with a pregnancy test even though that was highly unlikely to be the case. Ended up at the doctors who said it was an ulcer, probably caused by the cheap painkillers I'd taken. Took a good few weeks to get back to normal and was in a hell of a lot of pain.
I felt horribly horribly sick with it as well so get checked out just in case.