muffled hearing & blurry vision during pregnancy

hi mommies! today at 16 weeks pregnancy, i took the usual bus ride to work. i was standing for 15 mins as the peak hour did not allow me to sit. suddenly, my hearing became muffled and my vision was blurry (spinning at slow speed). this occured for a good 1 minute. i was so scared i would faint in the bus but thankfully it got better. has anyone experienced this before? is it due to low bp/ sugar? i did have my usual breakfast (maternal milk and 1 slice of bread) before leaving the house. #pregnancy #health