How low is too low? Net cals.

Okay. Hi everyone. I am new to MFP as of August 1st. I am not a stranger to weight loss, but new to this site and community.

I have been up well over 300 pounds in the past. I have lost 120 pounds in the past as well. I have gained back some, but not even half of what I had lost. I totally own that. My mother had taken ill, I was caring for two households, holding down my own, job, caring for a special needs child, etc. I stopped caring about myself and was taking care of everyone else as well as comfort eating. I didn't care how many calories were in the homeade macaroni and cheese or the lasagna...I was scared my mother was going to die--food made me feel a bit better.

So now...my mom is up and around and I am ready to really dedicate myself to dropping the pounds I gained back.

I have been logging my food and my exercise. I have read a bit about eating back exercise cals or not, etc. I am under the impression that when you have a lot to lose, as I do, that eating back exercise calories is not as important,but when you are clooser to your goal and leaner--it becomes important to prevent "starvation mode". Apparently when you are more overweight you are not as likely to enter "starvation mode" because you have ample fat stores that the body goes to first. But here is my question....how many net cals is too few?

I know I am working toward creating a deficit of calories by eating less and moving more.; I also know that to lose a pound that deficit must be 3500 calories. But is there a point where my net cals are too low? For example, my net cals have not exceeded 300 this week. Monday I ingested just shy of 1200 cals, Tuesday I was like 1290 (ish). Today I know I need to eat a bit more because my cals only stand at 830-something right now....and I know I want to get at least 1200. But with my exercise....my net cals are low. Help a girl out with some good info, would you? THANK YOU!!!