A Funny Little Thing

So. I have a riddle for those of you who wish to know. Take as many guesses as you can, posting them as comments below, and in a few days I will post the answer. If perhaps there is some competition, I may just give a free prize (perhaps a picture) to anyone who can guess it, but only if people participate! So. Take a guess!
 (I made this up, so don't be too harsh) OH! And Jozlyn, no giving it away!!

What am I....
I am very contagious.
You can catch me just by passing by.
Anyone walking by can give me to you.
You can get me through a window.
You can get me over the phone.
If someone in the room has me, then you probably will too.
You can get me through the TV.
You can get me in a text.
I will exhaust you and make you tired.
I usually come in groups.
Can you guess what I am?