Provide your best answer for the following question. Give ONLY the answer, no other words or explanation.
For example:

Answer: <most likely answer, as short as possible; not a complete sentence, just the answer!>.

The question is: Bill was awaking, what was happening to him physiologically?
eyes opening
His body was starting to transition from sleep to wakefulness. His brain was producing alpha and beta waves, his heart rate and respiration were increasing,