It seems like this is too few calories in general, and probably along with that it would be natural for you to not get enough nutrients. Others in this community can tell you better than I, but in short, if you cut back food that much, you're likely to gain it right back.
Your profile says you’re a male, but could you, please tell us how old you are? Annie is right that 800 calories to not enough for most people.
Annie mentioned Vitamin C and scurvy, but there’s also a chance of too little Vitamin B-12, D, Selenium, Zinc, Magnesium, Calcium and other vitamins/minerals. It will depend on what foods you’re eating to make up the 800 calories, but there’s a good chance it’s still not enough to be healthy without supplementing.
The problem with weight loss and no exercise is that we lost muscle mass (use them or lose them), which can, ultimately be as bad as not losing the weight.
Also, losing large amounts of weight without exercise to build muscle can leave us with a lot of saggy skin that’s as unsightly as being over weight.
All of that said - and 800 calorie/day diet is not healthy for adults.