Joe Jonas -- Rushed to the Hospital with Pain in the Abs

Joe Jonas checked into an emergency room in L.A. while doctors inspected his abs -- for severe stomach pains -- 48 hours after Joe did some late night partying in Chicago.

A rep for Joe confirms he went to the emergency room at Children's Hospital L.A. on Sunday. We're told Joe was only at the hospital briefly ... and it's not clear what was wrong with him.

One potential hint -- on Friday night (into Saturday morning) Joe was out at a Chicago hot spot Board Room Nightclub (above) partying ... and performed the next night in Chi-Town.

Whatever the problem was ... Joe felt good enough to eat out -- we spotted him and his bro Nick leaving Katsuya last night. Sushi after stomach troubles? Risky, Joe.