There's nothing wrong with low calories in the short term, especially if you're feeling fine.

In the long term, I'd worry about getting in enough food to get in all your vitamins, minerals, and micronutrients (though much less so than SAD low-calorie!). I'd also worry about the risk of stressing your adrenals. How much other stress do you have going on in your life? If your life is otherwise low-stress, your body can handle it better.

Basically, if you start to feel awful, sleep terribly, or perform terribly, re-adjust your approach.