I was sleeping 8.5-10h per day and still feeling extremely tired. Also had a lot of mental problems to the point I was thinking of going to a therapist (I thought it was work related).

My doctor sent me to do sleep apnea tests and blood work, but turns out I was vitamin B12 and B9 anemic AND seems like I have mild sleep apnea as well (I have more tests booked). But taking vitamin supplements cured most of my symptoms in less than a week. I had horrible headaches for the first couple of days of supplements though.