To be a High Risk Offender and be facing a minimum 3 year ban, you have to have 2 Drink drive offences within 10 years.
That time runs from the date you were convicted for the first offence to the date you were caught for the second offence. (The 11 years that CJ1980 mentions is for The courts to be aware of the 10 years, if the case takes a while to come to court beyond the 10 year point) so if there was a 10 1/2 year gap then you are clear of the 3 year minimum rule.
If your PTSD and anxiety is particularly bad, and you can evidence that it would have affected your ability to blow, then you could consider pleading not guilty. The offence is ‘failing to supply without reasonable excuse’. The drawback to that is that the police might decide to report your circumstances to DVLA who could consider revoking your licence on medical grounds!
You may well fall into the lowest ‘fail to supply’ bracket of a 12-16 months ban. This is where there were reasons for failing to supply, but they do not amount to an actual defence….. and there is no particular evidence of significant intoxication.
If the police have evidence that you appeared to be intoxicated, from witnesses and the custody video, and your medical problems are not felt to have affected your ability to blow, then you could be facing a 17-28 months ban, but this can hopefully be avoided, or certainly kept at the lower end of that scale.
All the above can be reduced by up to 25% if you are offered in court the chance to attend a Drink Drive Rehabilitation Course. Make sure to ask for it if you are not offered, as the offer cannot be made when your case is finished in court.
Perhaps your starting point should be to write to the police station that you were detained at, giving your personal details and the time / date you were in custody and request that you be supplied with a copy of your custody record and the custody video. You are entitled to apply for this. You can then view how you seemed to be that day, and have a clearer picture of the events in the police station than you recollect yourself because of the stress that you were probably under.