Have Had Diarrhea For Last 5 Days And Nausea The

Have had diarrhea for last 5 days and nausea the last 2. Today I've almost passed out just standing up. Very dizzy very weak. The almost passing out has scared me. Also noticed heartbeat was going crazy during the passing out episode but got normal when I lied in bed. My wife checked my BP and was 120/80 lying down.