There are many reasons that you may be experiencing that. Too many to speculate. As the previous poster said, you really need to direct medical advice questions to an actual medical professional. That being said, I will say:
Are you dehydrated?
Are you eating a healthy diet?
Do you smoke? drink?
Are you getting enough sleep?
Do you have pre-existing health conditions: high blood pressure, diabetes, etc?
Anytime you are in a state of reduced health, you should always make sure that you are:
- Drinking enough water
- Eating healthy foods
- Not smoking
- Sleeping enough
- Reducing and managing stress
- Taking care of known health conditions
If you are doing all of that and still having issues, time to see a doc.