I wake up at 3-4 am and cannot fall back asleep

In short: this is a very common scenario, and it is usually about your weekly background, not one “bad” night.

Night awakenings come in different forms. Sometimes you wake up briefly and fall back asleep. Sometimes your mind switches on and you stay awake for an hour. The second type feels worse because it can feel like sleep “broke”.

Common triggers people notice:

• sleep debt and schedule drift (see Sleep regularity)
• stress and a packed day
• late dinner or alcohol (see How alcohol affects sleep and recovery)
• travel or time shifts (see Daylight saving time and sleep)

In a tracker this can look like more awakenings, lighter sleep, and a rougher morning. But the tracker rarely answers “why”. It shows the shape, the causes are usually in context.

If mornings also feel foggy, sleep inertia can be part of the story: Sleep inertia guide.

Related short answer: I wake up at night and cannot fall back asleep (short).