It looks like there is something wrong with your health. So, from what I know, your problem is perhaps resulted from your low BP, or physical fatigue. For now, you should try to get some treatment from the hospital, also, please try to pay attention to the balance between your work and life. Some vitamin pills, and a better diet, some exercise, adequate rest, are severely required if you want to recover.
It is quite a normal phenomenon. It may be caused by tight neck muscles. When you feel tired, you will find that your neck muscles are tight. And then they will compress the blood vessels to limit the blood leaving the head, which may lead to a lowered oxygen level in the brain. And that is why your eyes look black at that time. If you want to solve this problem, you have to relax your neck muscles. When you are working or studying, try to massage your neck in a rest. Or you can go to the window to take a deep breath and exhaling, do it again and again. It is a good way to relax your neck. I hope this worked.
When you are so tired because of working too late until night in front of the computers, your eyes surrounding blood circulation will go block. At the same time, your eyes nerves will be affected too. Your black eyes are not normal which means that your body may contain some toxic elements or bad blood circulation. You need to use the home remedy like warm compress to release the black eyes symptom.
This is really normal. People will get black eye when have worked too long time without a break. Because when you are overworking, your eyes always in a constant state of stressed. In this state, your eyes couldn't get a good blood circulations that caused melanin precipitation. So, if you work really hard, give yourself a mid-week break.