I will check into that caoiheme sweeny
Tossing his head and keeping it to one side sounds very like an avoidance technique, that's usually caused by pain or discomfort.
No he is the horse I lease not own he has a saddle that fits but no therapist
Have you had the saddle fit, or had any physical therapist out?
My horse likes to toss his head up a lot and keep his head to the rail and the rest of himself to the inside
He is in good shape and around 10 or so
I try leg yielding because he is crooked but he pushes me into the wall
Lunging is also a great easy for them to warm up and loosen their muscle from there you can see where they are stiff and be able to go from there as to how to fix the problem. If he is an older horse you can also put him on a joint supplement to help him a long.
Ride him a bit longer on his weaker side so that he can strengthen that side
Walking in hand is a great way to ease stiffness, along with hacking. As Delia has mention, manual stretching is useful, but only when the horse's muscles are warm. Stretching a cold muscle leaves it much more susceptible to injury.
What areas are stiff? Have you any supplements? Has your horse been diagnosed with anything?
Also you could try making them turn to the inside whelp keeping them on the wall. If you do try this cut the arena in half.
Hand walk daily, stretch their legs your self too