“Why would a child faint?”

11 y/o child (male) fainted while visiting his grandmother in the hospital. He has not been diagnosed with PTSD, epilepsy or any other disorders. He is a vegetarian and does not take any medications. He was not under any mind-altering substances and never has been. He was wearing a mask (possible loss of oxygen?). He has never lost consciousness suddenly before. Later, he told us he experienced blurry vision (he described it as seeing everything in light-blue) , and nausea. After fainting, he was totally fine for the rest of the day. No one else in the room experienced any symptoms such as blurry vision. He said before we went into the hospital that he did not want to go, but we did not know how severe this was. My question is, could it be possible for an otherwise normal, healthy child to faint only because of sudden mental distress?