You know you have been roleplaying in the internet when you:
 

Find yourself trying to use some body parts that aren't present in your mundane human form. For example, I, silrayn silverwolf, miss my wolfy tail and ears sometimes. I try to twitch my ears and wag my tail. I just hope no one tries to fly out there. *Hears an unpleasant splat as she says so*

• Find yourself using terms like LOL (Laughing OutLoud) in a face to face conversation to express yourself. Use of "grins", "laughs evilly" or "huggles" instead of doing the corresponding action are advance symptoms.

• Try to hurl a fireball, throwing knife or have a go at someone with your weapon, be it an ax, a sword, or a throwing-knife. Hopefully, you don't have any reproductions of the said article within easy reach while you deal with your temporary insanity. *silrayn laughs evilly carrying a flame thrower*

• Itch to type your reply to anyone while verbally conversing.

• Develop a split personality to deal with the difference between your online personality and your "normal" personality. This can be seen when your online personality develops into a regular voice in the head for you. Warning, try to curb the tendency as this may cause full-blown schizophrenia.

• Become your online personality.

Another whacked out player: What split personality, there is only one me! Radar the Bold at your service.
Of course you don't tell your fellow workers or classmates that they are in danger of being decapitated by the mailing list's number one psycho character. *gulps*
 
• Start to woo the player who plays your character's online sweetheart for real.

Silrayn:  You don't even know if I'm a girl and you're a boy --er-- I mean you don't know if the other player is actually the sex she/he claims to be.
Another whacked out player: No probs, I'm bisexual.
Silrayn: *walks away muttering with intervals of snarufrufruf under her breath about people who seem to fall in love with the drop of a hat not knowing who they're really with!*

Hope you guys enjoyed this admittedly short list of symptoms. If you've developed any of these, feel free to share. It's a wide world out there.*grins*