I have wasted so much of my life and lost so many opportunities for happiness as a result of trying to resist/fight anxious intrusive thoughts. I am now trying to adopt this approach:
Rumination never, ever, ever, ever, ever achieves happiness and peace. It will always be self-defeating. It is always like scoring an own goal. It is always like trying to put out a fire by pouring oil on it. If I ignore the intrusive thought, I will end up feeling thoroughly miserable and stressed, but what have I got to lose? Really I haven't lost anything because the alternative approach of trying to fight the intrusive thought will make me miserable anyway (even if I feel an initial relief). Since I'm going to end up miserable either way, why not take the path of least effort and just don't bother fighting?
It helps me to recall a story in the Bible in which the city of Samaria was under siege and the occupants were slowly dying of starvation. A group of lepers in the city decided to get up and go over to the enemy camp. Their reasoning was that if they stay in the city they will die of starvation, whereas if they hand themselves over to the enemy the worst that could happen to them is that the enemy would kill them, which is no worse than staying in the city and dying of starvation!