yes! energy you can't see can be toxic. in fact other people's energy just doesn't even belong in our space unless it's a mom and baby, or some intimate time.

these guys, your friends, their anger was so strong and nasty that you absorbed some, or maybe theirs was feeding off yours and drained you, and then got physically ill by it.

i think people sensitive to this sort of thing tend to avoid the regular world if they can. You can put protective energy field around yourself to deflect others' negative emotional or psychic energy. Energy follows thought, so you just think it, visualize it and it's there.