Summary of characteristics of sleep stages
| Characteristic | Wake | Stage 1 | Stage 2 | Stages 3 and 4 | REM |
|---|---|---|---|---|---|
| Electroencephalography | 8–13 Hz | < 8 Hz | K-complexes, spindles | High voltage, low frequency (about 2 Hz) | Slightly slower than wakefulness, similar to stage 1 |
| Eye movements | Rapid, blinking | Roving | Still | Still | Rapid |
| Muscle tone | Highest | High | Medium | Low | Lowest |
| Normal percentage of sleep | NA | ~5 | ~50 | ~20 | ~25 |
| Other important features | Transitional state | Growth hormone secreted; sleep walking | Classical dreaming state |
NA = not applicable, REM = rapid eye movement.