If it is in fact just sleep I'd feel quite silly, although I'm certain I imagined many situations in vivid detail and had them play out later. As for the substances, I had been drinking and there was a very miniscule amount of marijuana involved, as in I drunkenly tried to take a hit from a perhaps already finished joint. The hospital didn't find any of it in my system.
You didn't mention the nature of the "substance abuse".
Decades ago the U.S. army produced BZ, which was the military equivelant of LSD.
Feelings of "deja-vu" were common in test subjects for up to a year.
That being said, check your glucose levels. Both high and low glucose levels can generate these experiences.
Most of the time deja vu comes from not getting enough good sleep, believe it or not! Even tho you think you remembered all that jazz when you were in the hospital, more than likely you were feeling impressions and emotions associated with being in a semi-dream state. So, you take that person and a few months later he hasn't been sleeping worth a flip, he's tired and unhappy as a result, and he goes thru a day half-awake, and there's a good chance he's going to get that deja vu experience.
You see, normally, there is a split-second delay in comprehending what you experience, so fast that it's believed to be simultaneous. The longer it takes you to process information, the more likely you'll think you've been thru it before...which you have been thru it, only it was just a second or two before. You walk in a room, talk to someone, and you're hit with deja vu. This means that first (a) you experience it for real, and then moments later (b) you recognize that you're experiencing it. That will make you think you've already been through that, which in a sense you have, it's just your mind didn't record it instantaneously with your experience of it.
Soooo, let's say you think you've been getting eight hours every day for your entire life. Fine. But what is important is the kind of sleep you're getting, whether it's deep and sound enough to restore and refresh you. Yeah, I'd get pretty sick of that wierd feeling, too, so you gotta stop whatever in the world you're doing these days that is wearing you out, that is interrupting your sleep, stressing you out, just whatever might affect quality of rest. To help you rest better, try exercising regular, drinking plenty of water, eating well, making your sleeping room as comfortable as possible, and try not to eat or drink anything except water a couple hours before bedtime, all these will help you rest better and the deja vu thing should go away.
Obviously if it doesn't, visit a doc, he will be able to do a few tests and ask some history and decide if further investigations are necessary, as there are a couple disorders that can produce this effect that have NOTHING to do with sleep. But at your age, the most likely cause is sleep deprivation. Let us know how things go.