Stage 4 sleep. Stage 3 also often emits delta waves.
Stage 4. apex:)
The stage during which it is most difficult to wake someone is the "deep sleep" stage. During this stage, brain waves, breathing, and heart rate are the slowest.
Stage 1 is light sleep where you drift in and out of sleep and can be awakened easily. In this stage, the eyes move slowly and muscle activity slows. During this stage, many people experience sudden muscle contractions preceded by a sensation of falling.In stage 2, eye movement stops and brain waves become slower with only an occasional burst of rapid brain waves. When a person enters stage 3, extremely slow brain waves called delta waves are interspersed with smaller, faster waves. In stage 4, the brain produces delta waves almost exclusively. Stages 3 and 4 are referred to as deep sleep, and it is very difficult to wake someone from them. In deep sleep, there is no eye movement or muscle activity. This is when some children experience bedwetting, sleepwalking or night terrors.In the REM period, breathing becomes more rapid, irregular and shallow, eyes jerk rapidly and limb muscles are temporarily paralyzed. Brain waves during this stage increase to levels experienced when a person is awake.
Slow wave sleep occurs after Stage 1 and Stage 2 sleep, and prior to REM sleep. There is more slow wave sleep present toward the beginning of the night, while more REM sleep is present toward the end of the night's sleep. In slow wave sleep, delta waves are present on the EEG (Electroencephalogram), which measures brain activity. These waves are long and slow, as opposed to the sharp waves of Stage 2 sleep. It is ecause of the shape of these waves that the stage is called slow wave sleep.
Delta Waves (APEX)
Paradoxical excitement or paradoxical sleep is a stage of sleep (during REM) in which the brain and body systems are active while the body is physically at rest. This excited stage while at rest is why it's a "paradox."