PAWS is real. I've experienced it, others have experienced it, it's as proven as a non-tangible object can be.
It's easy to make sense of it as well. There's going to be an approximately corresponding return to baseline (or as close as you can get) as there was in moving away from it in the first place. What goes up, must come down and all of that. Some substances have a noticeably longer PAW syndrome than others, like benzodiazepines, but the mechanism seems to be the same generally.
Serious opioid withdrawal would often leave me with noticeable paws for 1- 1.5 months while methadone (maintenance) withdrawal lasted 4-5 months. After these stated times, it became to difficult to distinguish my depression, anxiety and anhedonia from before I began using. The only thing close to GHB that I've been dependent upon is alcohol. I drank 750ml per day of 80 proof liquor for several months, underwent a medical detox for approximately 5 days, and experienced slight paws for 2 - 3 weeks.
I've heard alcoholics and medical professionals both claim that the PAWS from alcohol specifically can last much, much longer.