I had a pilonidal sinus nearly healed. Then the whole thing opened up. Why? This thing is driving me crazy. I will get brain damage before this heals.

Not uncommon. Don't get discouraged it is a common problem in some almost heals and breaks down as you described. Keep the ares clean, take regular showers wash the area with soap and water, apply dressings go for follow up visits and be patient for couple of wks. It will heal.