Afternoon sickness?

bochelly

I've been eating 1200 calories for four days now. I'm 5'1" and 191 pounds. It seems every afternoon I crash on the bus ride to work, closing my eyes and falling asleep almost instantly. When I get to work (cashier at a very slow store), I begin to get a headache. I try drinking water or eating some fruits/ veggies, but it doesn't help. Today I'm feeling very nauseated and my stomach feels upset. All other times of the day, I'm fine! I have been doing more vigorous/frequent exercises (between 20-40 minutes of Tae Bo daily) since I started this diet. Is this normal? I get home at night and exercise before bed. Is this a normal reaction to the decrease of calories? I'm falling asleep the same time I normally do, and with the exercise I sleep much faster. Could I be not eating enough, or needing more sleep?