Heräämisvaihe

Heräämisvaihe refers to the initial stage of sleep, also known as Stage N1 or NREM Stage 1. It is the transition period between wakefulness and sleep, typically lasting only a few minutes. During heräämisvaihe, brain wave activity begins to slow down from the alpha waves characteristic of a relaxed waking state to slower theta waves. Muscle activity decreases, and breathing becomes more regular. Some individuals may experience hypnic jerks, which are sudden, involuntary muscle contractions, often accompanied by a sensation of falling. This stage is characterized by a feeling of drowsiness and a reduced awareness of one's surroundings. It is easy to be woken up from heräämisvaihe, and if awakened, a person might not even realize they were asleep. This phase is a necessary precursor to deeper stages of non-REM sleep.