It's a common problem which occurs due to stress and Certain times just due to hormonal changes or sudden change of water also and it's very much reversible.
You need to get intralesional medications being applied over the patch areas and you would get hair in maximum 3-4 weeks
Just keep in mind this is curable
Next Steps
Visit a dermatologist soon and don't take meds from anyone besides them
Health Tips
Don't worry too much as this will only add to your problems