Is this anxiety or hedydration?

I arrived in New York yesterday and it is hot, and I'm not use to it. I came from washington. I'm really dizzy and I'm hot. And I'm really really REALLY nauseous. I have bad anxiety when I'm taking Celexa for. I just started the medication yesterday so it hasent worked yet. What is happening? Please help because I feel awful and I don't wanna feel this way anymore. Ps. I'm 14