As i was falling back to sleep this morning i saw a flash of light. what could this be?

This may be a sign: of irritation and stimulation of the retina, the brain interpreting it to you as light. It might mean the retina is being tugged, even torn. Your safest option would be to call your Eye doctor and, after you've described in more detail what you saw, decide with her/him whether you need to be examined. Stay well:)

Many possibilities : If persistent floaters or visual shading see an ophthalmologist or get a referral to one. Some types of migraine can do this. REM dissociation of your sleep can do this by literally propelling your brain into dreaming sleep as soon as you fall asleep when you are sleep deprived. Most likely not a stroke, as these have been shown to produce persistent gaps in the visual field.