What could cause temporary vision impairment?

Many things: I am guessing that there was a drop in the vision for a short period of time, less than several hours and then restoration to normal. This is age and health dependent but could include vascular insults, embolic events, optic nerve dysfunction, hypotension and a variety of other things. If this has happened only once, you can wait it out but if it happens repeatedly, then see your ophthalmologist.