Can being underweight be fatal?

Just went to the doctor recently for chest pains, lately everything been hurting from anxiety, stress, whole 9 yards. I am 24yr old male, 5'11" and weigh a measly 98LBS from all this crap, been like this for a while too. last time I went to the hospital they threaten to put a "feeding tube" in my nose, scared the crap out of me. Is it really that serious?