BT mystery behavior

~16 inch BT. 5900ft lake in OR cascades. Didn’t seem gravid, sex unknown. No apparent signs of poor health and no sign of it being hooked and released. Lake snow free for a month or more. No other fish were doing this. Heavy wind developed earlier and this was in the calm part of the shoreline. Exhibited this behavior for more than 3 hrs until dark along about 200 ft of shoreline. No fish could be found in am. If spooked it took off like a healthy fish only to return. Zero indication of making a redd although it was around smaller gravel. K, here is the curveball. I also spooked a garter snake underwater clearly searching for food in rocks in the same area. It would dart off and pop up in the middle of the lake and return as well. BT seems like it is spawning, but not really. Seems like an unhealthy fish, but not really; then the snake. So wtf, food, health or spawning? Weirdest thing I’ve seen in some time. Also zero interest in my line, in fact the lake is usually a sure thing and I caught nothing.