Sudden diziness and vision blurriness.

I am 19 years old male, yesterday i was at airport (i didn’t slept for 19 hrs and i was exhausted and anxious) I was standing and all of a sudden i felt that my vision is getting blurry and i can’t focus, then i get dizzy like i was about to pass out and at that time my heart rate was getting low and there were ringing in my ears also i had cold sweats and nausea but i got better in about 30 seconds, then a doctor came and checked my blood pressure, blood glucose, O2 concentration... Blood pressure: 126/82 Blood glucose: 101 O2 concentration: 95% And 12 hours later i did an ECG and Echocardiogram (they were both normal) So what might be the cause? Is it something serious? Is it related to neurology?