There is definitely a Cannabis hangover, but it's a lot more subtle than an alcohol hangover, for example, and it's pretty hard to notice until you completely stop. I'm someone who used to smoke nonstop, all day, every day, so to me, the cure for a Cannabis hangover was just smoking more. However, after taking tolerance breaks, you can definitely see the effects. For the first day or two after I stop habitually smoking, I feel quite terrible, mostly mentally, but there are some physical effects as well (difficulty sleeping, loss of appetite, etc.)
As far as mental effects, it feels like some kind of floodgate is lifted in my brain, and an onslaught of thoughts races through nonstop, for days, catching up on all the time Cannabis had kept them at bay. When I'm high, my mind usually operates at a much steadier pace, not as manic or chaotic. Sobriety, especially long periods of sobriety, mentally puts me back into that state where my thoughts are rapid, constantly changing, hard to keep track of, hard to shut out or ignore. I have a diagnosis of OCD as well as ADHD, so it's fair to say that my brain isn't like a "normal" person's. In fact, I've had multiple people tell me that when I do use Cannabis, I don't get "high" as much as I just start acting like a "normal" person - think of stimulants in the treatment of ADHD. When a "normal" person takes an Amphetamine, they start tweaking. But when someone with an "ADHD" brain takes one, they just slow down and act normal.
I've never been one to smoke once in a while and then move on, so I can't comment on what a Cannabis hangover is like if you smoke one time during a month of sobriety - my use has always been chronic and habitual.
