Occasional dizzy spells with feelings of weakness and faintishness. It happens once in a while and I do not know the cause of this problem

I am a 24 year old woman and a week and a half ago, I woke up early feeling very weak, I checked my blood glucose and it was 5.1. While standing up, I felt extremely dizzy, and my vision was blurry and I felt very disoriented and like I was actually going to faint. I took some glucose and with an hour or two, I felt better enough to sleep.

For the next four days, I felt still felt weak and have limited activity. Now I feel better with occasional moments of the dizzniess and weakness.

My concern is that I do not know why this is happening, and I am currently in my last year of university. It has happened before, last year it happened the same way, except it lasted for 3 weeks and I was mostly in bed rest. I went to the hopsital then and the doctor was unable to identify what was the cause and gave me gastritis medication.

I don’t know what is causing this but I have been told that potential causes could be my PCOS, I have not had my period for four months, or my generalised anxiety. I would appreciate any help.

Thank you in advance.