I was lying down and I felt something like a sting in my arm. I washed my arm and applied alcohol. There is a red spot about the size of a half dollar and it is warm to the touch. Do I need to go to er or is there something I can do for this at home? It has been about 2 hours ago.

I'd go to the ER. Let us know what it is and what they did.

Where I live (northeast US) we would be kicked out of the ER with a stern lecture for this. We have no poisonous bugs or spiders.
Washing is good though - I didn't wash a bite a few years ago, got an infection through the large hole the bug made, and a raging case of cellulitis over my entire leg.