I'm age 27, have one wisdom tooth, looks to be horizontal in x-ray, upper jaw. is nerve damage likely during extraction? don't want to be numb forever

Hard to say: Important that you know that possibility. A 3d x-ray (cat scan) may clearly show the proximity of your tooth and the mandibular nerve giving the oral surgeon better information, prior to the procedure. Even knowing this, many 3rd molars like yours are removed without permanent "numbness" -a lot depends on the talent and technique of the surgeon.

Get a CBCT Scan 1st: Find an oral surgeon with a 3d cone beam scanner and before any surgery, this form of dental imaging will provide your surgeon with the exact position of your horizontal wisdom tooth and your mandibular nerve in 3 dimensions! this will let your doctor be very specific about your risk of permanent or partial numbness prior to treatment. It's not a guarantee, but is very accurate!

Likely no: Any surgery can potentially result in numbness, however, transient or longer lasting numbness following wisdom tooth removal is usually associated with the teeth removed from the lower jaw. Indefinite numbness in either jaw is a rare event and high risk cases can usually be determined beforehand. Talk to your surgeon about your concerns.

Paresthesia: If the wisdom tooth is an 'upper' tooth, I have never personally seen or known of an individual to have permanent numbness (paresthesia) from its removal. If the post incorrectly mentioned an upper instead of a lower tooth, permanent paresthesia is possible but very unlikely in the hands of a well qualified oral surgeon. An oral surgeon can discuss risk\reward of its removal. Get 2nd opinion.