Have you mentioned the anxiousness/nervousness to your doctor yet? It definitely sounds like anxiety and maybe panic attacks. There's a lot of helpful information here; browse around a little and I'm sure you'll find something you can use to your benefit. God bless!
Anxiety and stress definitely can cause IBS...it plays havoc on your stomach!!! Mitral Valve is not caused by anxiety....however, anxiety can instigate it and make it do that flip flop more often...When I get extremely anxious I get the flip flops terribly...when I am calm it is much more rare....
Seems to me you are suffering from anxiety....take deep breaths and welcome!
My anxiety started with IBS and then escalated to panic attacks. I have also been tested for MV and I do have a heart murmur. Hang in there!