No, it's really not sustainable. 1000 calories is way too much of a deficit, we are talking about higher chances of illness, and a gateway to more headaches, stress, sleep problems and plain dying.

You want to get atleast 1500 calories a day if you are aiming for a calorie deficit. Roughly 2000 calories a day would keep you at maintenance i.e. your weight doesn't increase much nor does it increase much. So if you want a slight deficit and slowly burn fat then 1700-1800 would be ideal, 1500-1600 is also usually not recommended but works too and sometimes faster results but ofcourse, there are some little side effects

Also, don't focus solely on calories, eat more natural foods i.e. your Veggies and fruits and cut on processed foods like sodas, cakes etc