That's certainly out of the norm...my rabbit has noticed in the weeks after using DMT, he's more prone to see things in his peripherals while driving; aka he'll think he sees a person or animal about to cross the road, so he'll slow down and look and nothing will be there. However, I think that's just due to his brain being over-sensitized.
He's also experienced flashbacks, but they've always been pretty transient; things waving and breathing a little, colors changing, etc. Never all-encompassing and always possible to ignore.
As far as me, there are only two times in my life that I can remember having full-blown hallucinations without any psychoactive substances. The first time was once when I was running a high fever as a child.
The second was during a meditation experience I had, assisted with a program called SBAGen. This program generates different tones to play in each ear, and your mind tries to average them, creating a wave-like effect (known as a binaural beat). The theory is that if you meditate regularly, then under a state of meditation your brainwaves can be synced to the generated wave and alter consciousness.
Since it's kinda long and only semi-related, I made a separate thread for it -
click here.