 [ Symptoms ] what can cause extreme drowsiness related to hunger  my husband is 34 has smoked cigarettes since he was about 15 and has recently started getting extremely drowsy when he gets hungry it is uncontrollable no matter what he will fall asleep when he gets hungry after he eats he is back to normal he was having chest pains pretty frequently for a while but since things in our life have calmed down a tad those chest pains have not reoccurred it is been several weeks since he has told me that he had chest pains  could this be hypoglycemia [ Disease ] yes they are related both hydroxyzine and diphenhydramine are antihistamines used to treat allergic reactions both cause drowsiness and dry mouth as side effects hydroxyzine is available only by prescription but diphenhydramine is available over the counter