Feeling out of breath and weak please help

Ok well I'm on day 7 of my fast and besides stomach pains I am feeling so so weak. I was at the post office today and I was standing in line...STANDING...and I kept having to catch my breath. I don't know why, I have done much longer fasts before and I have never felt this way, I had so much more energy before.

Even if I take a couple of steps I am very winded and want to lay down. I am worried! Is everything ok with me? I thought maybe if I ate I'd feel better so I ate a little salad and had a couple of sips of diet coke. I am very worried about this now...I am planning on fasting till next Friday!

Does anyone have any tips, words of wisdom?

I'm very scared!