What Caused Syncope With Weakness And Headaches?

hi I am 20 years old and for 3 days I wasn't eating well then I fainted and started shaking on the floor. I notice I was on the floor shaking and got up. I felt weak, my left arm felt weak too then I ate more and felt better on that arm. I Started to eat! then I started to have headache here and there. this never happened to me. Help!