Fainted all of a sudden. Be 50-55!

I was travelling in the train one evening, it was crowded I had no place to sit so I was standing talking to a friend. while talking my head started spinning, I wanted to sit but I couldn't, so I controlled, my dizziness reached to such a level where I fell down, one lady got me up, offered me some water... it didn't really make a difference. as soon as I got off the train, everything around me was negative, like my vision had become negative, my ears blocked, my couldn't feel my body. This has happened to me before also, but I have never fainted unlike yesterday. and its not that I hadn't eaten, I did eat, eaten well. I could never figure out the cause of this. I am a little over weight, I am 63Kgs whereas according to my height I should be 50-55