Can emotional stress make you lose 20lbs?

Yes: People respond to emotional stress in different ways. Losing weight is a common response. But you should rule out other physical issues if you lost 20lbs and don't know why. Looking into therapy is not a bad idea, even if it is just for an adjustment period. Best wishes.

It is possible: While emotional stress and depression in particular can lead to weight loss it is important to check also whether something is going on physiologically/medically. It's probably a good idea to meet with your physician first to rule out medical causes. If you are going through some emotional stress meeting with a mental health professional to learn how you can cope with your stress will be helpful.