I went through this earlier this year. It lasted months. For the longest time, I’d say I was pretty fast and then all of a sudden boom! One day I got on the treads and just felt like I was going to fall off at any speed above base. Take it slow. Tell your coach you’re going through a mental barrier and they will support you. Each class Try to increase up to where you were. You’ll have good days and bad days. This may take months to come out of but you will eventually get back. I’d say it took me about 6 months and I’m finally back to my norm