I had something SORT of similar happen at the peak of my heroin use, when I was doing a gram + per day. They weren't hallucinations though so much as... dreaming while awake? It's hard to describe. It only happened a few times, always when someone would wake me up or I was just waking up, or when I would start falling asleep and wake myself up. It was like I was awake, but still dreaming for a few minutes after waking up. I'm sure that made no sense. Like I said it's sort of hard to describe... I'm trying to remember an example...
Ohh okay. Here's one. For instance, I was in a pretty heavy nod when my boyfriend (now ex) called me. I picked up, said hello, and then asked him what he wanted on his hot dog. I hadn't even been dreaming about hot dogs. There were no hot dogs around. We had no plans for the near, or even far future, to obtain any sort of hot dogs. But in my befuddled state, I genuinely thought I was out buying us hot dogs and that I was meant to go have a picnic with him afterwards... except I was in my room.
Another time, my boyfriend (now ex -- same one) woke me up in the middle of a nap. Upon waking up, I said: "Make sure the schoolteachers don't kill the spider." He had no idea what I was talking about. Frankly, in retrospect, neither do I. But for about 5 minutes, I was adamant that some schoolteachers were trying to kill a spider, and I was determined to stop it. He finally managed to convince me that it wasn't real, that I had just been dreaming or something, and that there were no schoolteachers and no spider.
I never SAW the schoolteachers... the spider... or the hot dogs. So they weren't hallucinations so much as they were delusions. Very real delusions. The only time I actually hallucinated was one time when I was asleep on my bed and I woke up for whatever reason... forget why, probably just naturally waking up... and saw my exe's roommate's cat chilling across the room. I called the cat's name a few times before the image finally faded away and I realized she wasn't ever REALLY there. That was the only hallucination I had.
I would also wake myself up often by talking nonsense - I can't remember what I'd said now, but I do remember it was quite amusing to the people around me. Another time I woke myself up with the most bloodcurdling scream ever. No reason - I wasn't having a nightmare. I just screamed. The people around me were not so amused that time... I believe it was somewhere around 3 in the morning, and the person who's house we were at had their parents asleep in the next room.
It all stopped once I got back below a certain dosage though. It had to have been the obscenely strong shots I was constantly taking... that's the only explanation I can think of. Weird shit though. But yep, it seems if you do a lot of dope, it can definitely do that to ya.