By you posing the question, I think you know the answer...yes, in my opinion, you can very well easily fall down the rabbit hole into an eating disorder.
900 calories a day is NOT ENOUGH! Please eat more. 900 calories a day for ANYONE is unhealthy, damaging to the body, and unrealistic. You need to consume MORE calories than your resting metabolic rate, and based on your weight and height, your resting metabolic rate is probably around 1400 to 1500. That means that you need to consume that many calories per day just for basic bodily functions like your central nervous system, digestive system, maintaining core body temperature, etc! You are doing your body a disservice. You are not giving it the fuel it needs to funtion properly. You'll start to feel lethargic, your heart, brain, lungs, liver, kidneys will strain itself just to keep you alive, your hair might begin to fall out, you'll feel cold all the time when no one else does. You are not getting enough nutrients at 900 calories a day! You'll start to get sick easily, and you'll become deficient in vitamins and minerals. Are you scared? I hope so! My hope is that you'll be scared into EATING!
I think you need to scratch dieting for now. Find out how many calories you need to MAINTAIN your current weight. Consume that amount of calories! Please! Better yet, don't count calories for a while. Go by how you feel when you eat...listen to your body when it tells you it's full. Think back to a time when we humans didn't know about calories as a unit of energy, when we just ate real food and stopped when we were full.
What you are doing right now is damaging your body. Instead of focusing on calories, focus on eating whole, unprocessed, nutritious foods! Make cooking healthy meals your obsession!