I know that if I get below a certain number of calories/day I get pretty cranky. My magic number seems to be 1,100 - if I go below that for more than two days, I start to get tired, headaches, grumpiness, etc. -- so whether I am in a "starvation mode" or not, I'm not a pleasant person to be around regardless!! But I think that if that did not happen to me, I would go below that 1,100 plateau fairly often, as I can feel very full on 1,000-1,100 calories if they are high-protein.
I think if you're listening to your body, feel energetic and healthy, then you're probably doing just fine. If you feel lethargic, dizzy, or have other health symptoms - talk to your doctor.
Female, 28 years old, 5'4 1/2" tall
Starting weight 1/4/11 = 215.2 lbs.
Weight 9/3/12 = 164.9 (net: -50.3 lbs.)
Current mini-goal: 160 lbs.
Next mini-goal: 150.2 lbs. <--- Official "Healthy BMI" weight
Estimated final goal: 130 lbs.
"You don't have to change your life today. You only need to change your day today."