upper stomach nervousess/cannot breath/ bp drops oxygen drops, no one been able to find reason

MY MOM IS 82 YEARS OLD,SHE HAS BEEN A PRETTY HEATHY AND ACTIVE WOMEN EVEN AT THIS AGE.

SHE HAS BEEN TO THE EMERGENCY ROOM SEVERAL TIMES IN THE LAST FEW WEEKS. MOST OF THE TIME SHE FEELS VERY WEEK AND AS SHE SAYS FEELS FUNNY(HARD TO EXPLAIN SHE SAYS)  INSIDE AROUND THE TOP OF HER STOMACH SHEGETS VERY NERVOUS FEELING. SHE CANNOT BREATHE.

AT THE ER HER BLLOD PRESSURE HAS DROPPED,OXYGEN TO LOW. THEY KEEP HER FOR SERVERAL HOURS THEN THEY LET HER GO WITH NO ANSWERS.

PLEASE HELP, I AM AFFRAID NEXT TIME MAY BE THE LAST.