I don't know how long you've experienced this, but I've heard that with a lack of good sleep for a long time, that lack of sleep can be "made up" by excessive sleep. But excessive sleep often causes one to be tired throughout the day. Idk what you can do though...
It seems to me that your body is trying to adjust. Sleep deprivation will eventually take its toll and you'll find yourself unusually sleepy, just like what you were experiencing. But if you feel that you have enough sleep but still tends to be sleepy then maybe it's not the lack of sleep. How's your diet? Do you take any supplements or any medication? Sometimes too much caffeine can have the side-effect of drowsiness, maybe you've ingested a lot of energy drinks rich in caffeine. If you really want to make sure you can actually have yourself check. i would also recommend that you check your sugar level. I hope this helps.
See your doctor and get some bloodwork done.
Ferritin, Vitamin D, magnesium, B12
Check your vitamin D levels with 25OH vitamin D blood test. Low D and low magnesium cause cause fatigue, insomnia, anxiety, depression, dizziness, body pain, headaches, etc.
You want you D levels above 50ng/mL. You can supplement with D3 and magnesium