Can't speak for la cocaina, just booze. I've never been to a treatment center, but I've tapered myself once and quit cold turkey twice (which is a dumb idea if you drink a lot please don't do this get actual help).
Tapering is just drinking less and less each day, it's not to get drunk necessarily, but to stave off the detrimental effects of alcohol withdrawal (ex: day 1 of your taper you drink 23 beers instead of the full 24 pack, then 22 the next day, then 21, etc. etc.). You have to have a lot of self control to do this, which is why most people choose cold turkey or go into an actual program.
Cold turkey is usually a nightmare, but it depends on how much booze you've been drinking and how long you've been doing it for.
I had brain fog, shakes so bad I couldn't walk, was constantly sweating, constantly dry-heaving, and couldn't keep any substantial amount of food or liquid down for the first few days. I was also having audio and visual hallucinations, imagining whole scenarios in my head that I thought were 100% real. Basically all the symptoms of Delirium Tremens.
I also couldn't sleep during this period, which probably doesn't help with the hallucinations. The best way I can describe it is if you've ever had a dream where you fell or tripped, and your body spazzed and you woke up? During withdrawal this happens every time your body gets close to entering REM sleep, so you never get any actual rest.