I've hasd an ab strain before. i was doing fine one moment and next i could barely stand up b/c of the intensity of the pain. the funny thing was that I wasnt training abs at all. i went to the E. R I ask the nurse, you know the one that does bolld pressure and ask you about whats wrong before you go in the room. He told me that it was mostly likely a strain.. when i got in the E.R. room. they run alot of test b/c there could be a lot of things i.e. kidney/liver stones and etc. after all that. they couldn't find anything wrong. so, they just told me I had a muscle strain of the abs. and just take some pain killer. I was fine a week later..
but see a doctor if theres any underlined probems with your stomach/abs area...hoply its a stain. a strain is easy, to take care of the anything else.