Feel like im going to faint in the heat!!?

ermm i went to london today, trouped through trafalgar square in the heat and my uniform wat thick kiniitted cotton-compulsary- ive just come home, i cant get cooler, i feel quite tired and as if i need to lie down NOW! ive had drinks but nktohign is helpinhg i can't concentrate that well like right now i have to go back and correct words, i feel light headed and as if imma get a headache, im really clammy and i feekl sick how can i not feel klike this/?