Anxiety for no reason

I have severe anxiety usually I know what triggers it and how to control it if I start to have an attack but here lately I have been becoming anxious and not being able to figure out what the cause is. Example today I was with my boyfriend fishing as we’ve done a thousand times and all of a sudden became very anxious. I am not sure what caused it and haven’t been able to get rid of the feeling. Any suggestions or ideas on why this might be happening would be a big help.