Hi. lately i have a weird feeling underneath my chest. almost feels like my diaphragm twitched. it feels like a hiccup but only in my chest. it didn't happen when i was on antidepressants.what is it?

As above: It is not easy to make a decision what is going in without examination. I suspect anxiety, if u feel bothered see u physician or a mental health professional for evaluation.

Anxiety: Hard to say for sure, but if it wasn't present on an anti-depressant then it could be anxiety. A hiccup is a sort of "diaphragm twitch", so that of course is another possibility.