For 4 times, my vision get clouded with yellowness suddenly, i can't find my balance and i feel nauseous. had to sit down but comes back when i stand.

See doctor: This may happen with severe anemia (more likely in a female with heavy menstrual flow and little iron intake) or even migraine. Need to check with doctor. I presume that you were not dehydrated during these episodes since this can be one of the causes as well.

Hypotension: This is a syndrome that can be caused by abnormally low blood pressure and the symptoms are cleared by lying down. Check your blood pressure sitting and then standing after 30 seconds to see if your blood pressure drops below 90 systolic and produces your symptoms. If this is the problem, get evaluated by your physician for conditions like anemia, neuropathy, iron deficiency,etc.