system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Is it possible to be tired from too much sleep?
gpt
There isn't an official reason why this is, but there are some speculations on why it happens. 

If you sleep for 10+ hours, that means you didn't drink any liquid for 10 hours and whatever liquid you had prior to going to bed are in your bladder. Dehydration is known to cause dizziness and headache, which could feel like being tired. 

Also people often sleep too much during the weekend to make up for too little sleep during the weekday. Irregularities in sleeping schedule tend to cause tiredness too. 

Another possible reason is your body produces too much melatonin when you sleep longer than intended, that extra melatonin will take longer to dissipate after you wake up.