From my personal experience, sleeping too much made me so lazy and unmotivated whilst sleeping just enough made me feel more energized, motivated & productive. I don't know the science behind it but it's something I learned from personal experience, try it for yourself & see what works best for you!
It most likely will affect your natural circadian rhythm, but I think too much sleep, rather being a cause of something bad, is usually a symptom of a larger issue. Many people who are sleep deprived have a tendency to “binge sleep” when they have weekends or vacations, but this type of sleep pattern is not healthy. Some studies have also shown a correlation between depression and sleeping more than usual. Fatigue in general can be a side effect of many physical and mental health issues. If you are worried about how much you are sleeping, or irregular sleep patterns in general, I suggest you visit your doctor. They will know what diagnostic questions to ask and tests to administer in order to see if you have an underlying issue causing your sleepiness and provide you with next steps to help you get back on track.
It almost has the reverse effect. Instead of feeling rested you will feel exhausted when you get up. Wanting to stay in bed for too long can also be a sign of depression or other health conditions.
I am an expert on this subject. When I sleep too much I feel more tired the next day and sluggish. I feel anxious because I have less time to do things and then guilty because I didn't get much done that day.
I have multiple sclerosis and in my life, there is no such thing as too much sleep and a lot of sleep can ONLY be a good thing
I think amount of sleep is as unique as our inviduality. Find out what makes you feel rested. Sometimes you can oversleep because the quality of sleep you had for the first few hours was poor and your body still needs to recuperate. Personally, warm tea and meditation make sleep like a baby.