They're probably not complete junk, just a combination of herbal stuff that didn't agree with you. Most over the counter fat burners contain stuff like caffeine, green tea, guarana, bitter orange, capsaicin, grapefruit seed and other stuff that supposedly 'assists and increases fat burning'. What has the most effect out of all these ingredients is the caffeine, which firstly suppresses appetite and secondly elevates metabolic rate. You've probably just had a bad reaction to a high dose of caffeine taken in combination with a bunch of other weird stuff you've never ingested before.
I'd agree with everyone else that you're best to lose the weight the natural way and not bother with the pills. They're not total junk and used as per the instructions most of them do increase fat loss very very slightly, but why pay the extra for something you don't actually need and can do yourself?