For some people it is a phase and for others it is permanent. I would guess that this is probably a phase for you. Personally, I lose a little bit of my vigor every winter because I have had bad riding/horse experiences in the cold and dark, but I am better by the summer. I also get discouraged if I have a horse on stall rest, I can't ride and they get harder to handle. But I stick to it and wait for things to get better. If you feel that you need time off, then you need time off. You can send him off to a vacation barn or have someone lease him, it is better that you take a break and come back than to stay unhappy and stressed. Nobody is forcing you to make any choice, all that matters is your horses health and your happiness. Whether that means working with him more or leasing him out is up to your heart.