Do you take any medication?
What is the appearance of the eye and the lid at the moment?
Is there any pain or unusual sensations?
Is there any bruising elsewhere, or any small burst vessels in the eye itself?
The eyelids are incredibly thin and lack the sub dermal fat that tends to cushion skin in other areas. Trauma could have occurred accidentally through rubbing the eye without realizing.
Bruising occurs when there is a deficiency of iron, vitamin C or in some anemia problems. The fact that you are tired indicates that you need to have a full blood count to look at your platelets and their function as well as levels of iron, vitamin B12 and folate.
Some medication such as aspirin and warfarin cause spontaneous bruising through their effects on platelets and clotting however you do not mention any use of these.
If the problem lasts for more than 2 weeks then you need to have it examined for other possible skin lesion.
So I would recommend that you see a doctor for some blood testing and in the meantime you could take some arnica tablets for the bruising or use a cold compress for the swelling.