Oxymetazoline
"I tried this product as a result of a bad day of allergies.  It worked as advertised, clearing out my sinuses effectively.  However, I did not read the directions thoroughly and used it for 3 days.  After I stopped, I suffered the rebound congestion, and it was horrible.  I nearly gave in to the temptation to use it again, especially since I couldn't sleep with the congestion.  Luckily, I found a simple alternative--BreatheRight strips.  They hold the sinuses open nicely, allowing me to sleep without turning to Afrin again.  Hopefully, the condition will go away."