Experiencing erectile dysfunction out of the blue. What the hell? Is it my mind or body?

Could be both. Most commonly men who have sudden onset of ED have inhibition as a result of some event- anxiety, pain, distraction, alcohol, fatigue. But there may also be excessive nerve tone expressed by the brain which contracts the blood vessels making an erection harder to obtain. This can be psychologically and/or physically activated. Either way it's complex and it the problem persists visit a urologist.
Erectile dysfunction. In a case like yours, top of the list of things to consider is drug side effect: Did this follow the start of a new medication. E.g. beta-blockers (propranolol, atenolol, metoprolol etc) are well known to cause this.