I had a reaction last year when I bleached my hair. It burned. Now I've lost over half of my hair from the scalp. I'm worried?

having a consultation with a hair transplant surgeon can help determine if your hair loss is permanent or not. A thorough consultation with a surgeon will examine your scalp, and review the nonsurgical and possibly surgical options that you have. 

This is all too common nowadays and I feel this scenario is increasing. I would advise you see a dermatologist specializing in hair loss for guidance. You may need anti-inflammatory treatments. My approach involves a careful review of an individual's medical history, and review of the scalp via dermoscopy. I usually perform a scalp biopsy in these situations because I do feel that inflammation and scarring is what leads to hair loss in many such cases of burning after hair bleaching. If it's been more than a year, there may or may not be much regrowth possible but I can't say for sure for any given person without seeing the scalp.  I generally use topical steroids and even short courses of doxycycline for individuals with inflammatory or pauci-inflammatory scarring alopecia secondary to such burns. We're seeing more and more cases of permanent hair loss from scalp burns secondary to bleaching and highlights.

bleach and chemical burns to the scalp can cause permanent hair loss. You should see an expert for an opinion as to the degree of hair loss that you have and if it is irreversible.