Since I'm getting sleepy... tell me the stages of sleep and what should be normal in young adults, and what changes occur in the elderly?

There are four stages, and in young adults....
stage 1: 5%, light sleep
Stage 2: 25%, Deeper sleep
Stage 3-4: 45%, Deepest, non-REM sleep; sleepwalking can occur, along with night terrors, bed-wetting (slow-wave sleep)
REM: 25%, dreaming occurs, loss of motor tone, possibly a memory processing function (we need REM for the night before the USMLE), Increase Oxygen use;

Elderly: decreased REM, decreased slow-wave sleep, increase sleep latency, and frequent awakenings during the night