One great danger with sleeping too much is that makes you leave the things you should have done undone which is a great danger to basic life accomplishment.
By the time you develop the habit of postponing the things you should do at the moment until later, it begins to tell on you negatively.
Excessive sleep has the power the power to make you loose opportunities, when you sleep all the time, it makes you postpone opportunities and keeps you at a low and stagnant position which makes you unable to move forward.
Excessive sleep could cause over weight gain which could result into obesity, by the time you spend almost all the hours of the day sleeping, you become really fat and you will not even be happy with your self.
Sleeping too much can cause dizziness.
Sleeping too much can cause depression.
Sleeping too much can produce a high level of stroke.
Sleeping too much could result into pain.
Sleeping too much could increase the level of heart disease.