Montelukast
"I have chronic postnasal drip. I have had no success with OTC allergy meds. My ENT decided to try generic Singulair. First night I was wide awake all night and had uncontrollable muscle tremors & twitches. The next day I had headache,  stomach ache, heartburn, & terribly dizzy. Next night I had difficulty sleeping, terrible vivid nightmares, night sweats . Woke with low fever, as well as all those other symptoms,  Felt teary for no reason. Thought I had the flu but when looking up if 'sweats & nightmares' are Singulair side effects. I found ALL my issues were! Tried to stay with Sigulair as I knew it was one that needs to build up, but after a week & no effect on my drip it was too awful to bear any more. Was not good for me unfortunately."