What Causes Fatigue And Dizziness In A 31 Year Old?

Hi I'm a 31 year old woman and for the last week I've Ben suffering from fatigue and dizziness. I am off work and resting and my energy levels have improved but I have this strange feeling in my head which won't go away. It's not a ache or pain or dizziness, infact I'm not sure how to explain it. I have to keep lying down as it's worse when Im upright and move around. I have underactive thyroid and the doctor did blood test the other day. Not all the test results are back yet but something has shown up with my blood sugar levels and they want me back in for a fasted blood test. Is the strange feeling in my head connected and is there anything I can do to relieve it?