How to manage intrusive thoughts, especially if it makes you feel anxious in certain situations?

Mindfulness can be a great tool in personal experience. The idea of taking the thought and placing it on a leaf can be helpful. Once you've placed the feeling on the leaf in your mind then set the leaf in a river of flowing water, watch as the thought goes farther and farther away. Breathing techniques can also be very helpful! Try breathing in for 8 seconds, hold for 4 seconds, breathe out for 8 seconds, and hold for 4 seconds. It can feel a bit strange at first, but the breathing technique has a very calming effect on whomever decides to try it.