allergic reactions
"Chlorpheniramine right before bedtime does 2 great things for me:  (1) reduces allergic build up during sleep (if my hay fever is bad one day or my asthma increasing, often I think back and realize I forgot to take it the night before) and (2) helps me feel drowsy (a normally unwanted side effect that becomes an advantage at night).  I take the 12 mg extended release table and really suffer if I run out. GREAT!"