William Vallicella wrote:
When I wake up from a dream I realize I was dreaming; but when I go to sleep and dream there is no parallel recognition that I was awake.
Serious philosophical juice can be squeezed from this observation. Some other time.
[From Maverick Philosopher: Dreaming and Waking]
He could have added (some other time?), there is no brain in the vat that catches this juice.