What is this feeling I have?

Today a couple of guys came over to fix my computer.This one guy came in and said hi, as soon as I looked at him, I couldn't stop smiling.Their gone now,but my heart is racing, I'm sweating.And I just feel strange.I never felt this way before.What's happening to me? My heart is literally racing, and I can't stop thinking about him and how I couldn't stop smiling.I had to hide my smile.I don't know what's happening to me but I feel strange.