I like sleeping when it is raining because it is much cooler and the body tends to seek the warmth and comfort of the bed or even another human’s hug and body warmth. The calming, relaxing, and soothing sound of the rain dropping on the rooftop is music to my ears. The sound just hypnotizes me to sleep like the symphony of nature. Relaxing sound makes me sleepy.
Rain is related to atmospheric pressure. When raining, atmospheric pressure is very low and it is making us sleepy and tired. It’s darker when it’s raining because the rainclouds cover the sun, so even if it’s daytime or whatever time of day, you would feel as if it’s still dawn.
Since you wouldn’t have a way to do several activities outside for fear of getting wet or muddy, then what else could you do but rest, and the best way to rest is indeed to sleep!