Why does sleep sometimes feel heavy instead of restful?

Sometimes I sleep for what feels like enough hours, but I still wake up feeling exhausted.

It’s hard to explain, but the sleep itself feels heavy. I’ll wake up with that groggy feeling like my body is awake but my brain is still somewhere else. Some mornings I feel more tired getting out of bed than I did before I went to sleep. It’s confusing because I always assumed more sleep automatically meant feeling better the next day, but that hasn’t been true for me lately. There are nights where I sleep less and somehow wake up feeling more normal than I do after a longer sleep.

I’m trying to pay more attention to things like what time I sleep, whether I wake up during the night, and how late I use my phone, but I still can’t figure out what makes some nights feel so much worse than others. Do you ever wake up feeling exhausted even after sleeping for hours? What helped you get out of that cycle?