You do not want to admit that you lied as this is grounds for the guard to prosecute you for fraudulent enlistment. If you do apply for WOC School and during the course of medical qualifications and the medical issue that you lied about becomes apparent and you deny knowledge, this will probably wind up being a false statement. Either way, both possibilities will most likely subject you to prosecution under the applicable laws of your state's code of military justice provisions (which usually follow the UCMJ) or to UCMJ action if you are on orders pursuant to Title 10.
A difficult situation, you need to obtain counsel before you make any decision here.
Concur with Attorney DeWitt--I would only add that you will have a military X-ray someday, maybe at your separation physical, and eventually they will find out. More importantly, if the coil (I am unfamiliar with it) is something that should disqualify an applicant, it's likely because there is a significant health risk associated with the coil and military service, you may one day find yourself in the scenario that gives rise to the risk.
Recommend you see an attorney and handle it now before you get busted, or seriously injured.
READ THIS BEFORE CALLING OR EMAILING ME: I am licensed to practice before the state and federal courts in Virginia. Addressing your issue does not create an attorney-client relationship and I AM NOT providing you legal advice. You should speak with an attorney to whom you have provided all the facts, before you take steps that may impact your legal rights. I am not obligated to answer subsequent emails or phone calls unless you have hired me. I wish you the best of luck with your situation.
I agree with the other posts but there may be another option for you. In my experience, a failure to disclose a fact such as you have hid more often leads to a discharge than a court-martial or non-judicial punishment. Some branches (at least the Air Force) allow Commanders to waive a fraudulent discharge under certain conditions. This most often happens where you have been a good military member, your unit likes you, and you've given them enough reasons to want to keep you. I suggest you consult with counsel who can walk you through the potential waiver and evaluate whether its worth the risk. As the other attorneys have said, you do run the risk of a criminal charge but you may be able to avoid it in the right situation.
Providing this general response does not create an attorney client relationship.