The sense of anxiety and/or dread one feels when an IM is left unanswered for more than approximately 30 seconds. Generally this occurs at the beginning of a relationship when the other parties feelings are in question. IM anxiety may be accompanied by unreasonably frequent glances at the IM window and an utter inability to perform any non-computer tasks.
I was getting crazy IM anxiety yesterday when she wouldn't answer on MSN. Turned out she was just doing housework >.<