I fainted in the shower, today, after blowing my nose extremely hard. should i be worried? should i go get checked out in the emergency room?

No: Talk this over with your regular doctor. There are a number of reasons why people pass out. A good start would be a holter monitor (basically, checking out your heart activity for 24-hours) and an echocardiogram.

Many causes of faint: There are many causes of fainting. Most are not dangerous. If you are feeling well, please call your doctor for a check. If you are having continued symptoms then consider getting more immediate evaluation.

Valsalva effect: A reflex causing extreme slow heart rate, even a brief absence of heart beats. Next time in shower if you have a lot of snot, suck water up your nose, then blow out only ONE SIDE. Not too hard!!! Better a few smaller blows instead of a single big one. The water will loosen the material so you can get it out without stopping your heart.