From everything I have heard and read, I am going to assume benzo's (never W/D from them myself). I do have anxiety and have had panic attacks, so I know how bad that can be. I can only imagine going through that for weeks on benzo W/D. I'd probably end up in jail for robbing a pharmacy.
Right now, I am on day 3 of Effexor W/D and let me tell you, I will never take another antidepressant. It's so bad I got 600mg of Oxy and 300mg Diazapam sitting right next to me, but I am too sick to touch either. All I do is drink 7UP and eat corn chips and mild salsa (which is strangely relaxing and easy on my stomach). That and crap, stumble around from the dizzyness, hear things that aren't there, stay awake for 40-50 hours at a time, and just generally feel like runny shit on a slice of burnt toast. It's like a really bad flu with delerious fever, body aches and a compelte inability to do anything that requires active thought without considerable force of will to concentrate.