Stage 1 - This is where the baby goes from being awake to asleep, rather quickly and short. Here the breathing slows down, the muscles tend to relax, and the waves of the brain slow down.
Stage 2 - This indicates light sleep, that is, just before the later deep sleep. Here, the heart and the breath further slows down and the muscles relax more as compared to before. Adding to this, the movement of the eyes under your lids stops and the activity of the brain slows with sporadic periods of electrical activity.
Stage 3 - In order to feel refreshed, this stage of sleep is required. It occurs more in the first half of the night where the brain waves, heartbeat, and breathing are at the lowest point.