I just stumbled across a fascinating 2002 paper where pioneering sleep researcher Allan Hobson describes the effect of a precisely located stroke he suffered. It affected the medulla in his brain stem, important for regulating sleep, and caused total insomnia and a suppression of dreaming.
In one fascinating section, Hobson describes the hallucinations he experienced, likely due to his inability to sleep or dream, which included disconnected body parts and a hallucinated Robert Stickgold – another well known sleep researcher.
Between Days 1 and 10 I could visually perceive a vault over my supine body immediately upon closing my eyes. The vault resembled the bottom of a swimming pool but the gunitelike surface of the vault could be not only aqua, but also white or beige and, more rarely, engraved obsidian or of a gauzelike nature mixed with ice or glass crystals.
There were three categories of formed imagery that appeared on these surfaces. In the first category of geologic forms the imagery tended to be protomorphic and crude but often gave way to the more elaborate structures of category two inanimate sculptural forms.
The most amusing of these (which occurred on the fourth night) were enormous lucite telephone/computers. But there were also tables and tableaux in which the geologic forms sometimes took unusual and bizarre shapes. One that I recall is a TV-set-like representation of a tropical landscape.
In category three, the most elaborate forms have human anatomical elements, including long swirling flesh, columns that metamorphosed into sphincters, nipples, and crotches, but these were never placed in real bodies.
In fact whole body forms almost never emerged. Instead I saw profiles of faces and profiles of bodies which were often inextricably mixed with penises, noses, lips, eyebrows; torsos arose out of the sculptural columns of flesh and sank back into them again.
The most fully realized human images include my wife, featuring her lower anatomy and (most amusingly) a Peter Pan-like Robert Stickgold and two fairies enjoying a bedtime story. While visual disturbances are quire common in Wallenberg’s syndrome, they have only been reported to occur in waking with eyes open.
Blurring of vision (which I had), and the tendency of objects to appear to move called oscillopsia (which I did not have), are attributed to the disturbed oculomotor and vestibular physiology.
Link to locked report of Hobson’s stroke.
Mind Hacks 
This is truly fascinating. But what I find equally interesting is that he could save the memories from hallucinations and describe them later on with such detail. I am not sure if everyone can do that. It could have been that as a researcher, his brain was trained to observe, collect information and describe them at a later time.
From the linked paper “substantial recovery occurs” in the brain. This is good news as most people think the brain can not heal from injury, when sometimes it can.