To sleep, perchance to dream

This is a strange thing, and comes into the category of you don't know it was gone until it comes back, but I've started dreaming again.

Pre-treatment I slept heavily, and crashed for a couple of hours a day minimum, but I have no memory of any dreams. This may be because I slept so deeply that I could not be woken during the dream phase of sleep, and now I can. Or it could be a partial explanation for the cog fog. I was not sleeping properly, dreaming and so processing  the input to my brain.

"REM sleep time is strongly reduced by hypoxic and increased by hyperoxic atmosphere, in accordance with the existence of an O2 diffusion limitation. Any pathological decrease in arterial PO2 and/or O2 delivery creates a specific risk in REM sleep."
http://www.ncbi.nlm.nih.gov/pubmed/11382905

Durring REM sleep, there is an increase in blood flow to the limbic system and the brain stem, with circulation to these structures decreasing during non-REM sleep.  As brain activity increases during REM sleep, the cerebral requirements for glucose and oxygen both increase....
Fundamentals of Sleep Technology--Butkov, Lee-Choing  2007

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I would be interested to hear your experience. Do you dream?