The Path of the Horse is contraindicated for...
excerpt from Wightridden: Paths of Northern-Tradition Shamanism
1. People with trust issues. If you find it difficult to trust even people who love you and are reliable, you will not have the ability to hold yourself open for the god to enter. You may react instinctively, slamming the door shut instead of being responsive. Work on your trust issues, including any anger you may have towards the Powers That Be. If you are blaming the Divine Will for your problems, you won’t be comfortable with letting any aspect of it run your body even more closely.
You can work on trust issues with the aid of other human beings. Ask the people who you trust the most to blindfold you and take you somewhere unknown, perhaps to do something that you have never done and have no knowledge of. If the idea makes you recoil, you’re not ready to work with god-possession.
2. People with poor boundaries. You need to be able to set boundaries, or you’ll just become a powerless vessel, living your life around the visitations of your patron deity. It’s hard to do things like hold down a job or have relationships or care for children when you’re constantly being used as a horse. If you want to take this path, you will need to work on the firm mental negative. It’s difficult, because it can be an amazing feeling to share your vessel with a Power, and it’s hard to turn down, but if it’s getting in the way of your daily activities, it can damage your life and health and make you a less worthy vessel. This is in addition to the fact that a deity can better be served and honored if the right situation is prepared for it in advance - which is something that most Gods can understand when you use it as a reason - "If you wait until next week, I will have a ritual set up, with your favorite foods and people to interact with! Please allow me to honor you properly!" But don’t let it take over your life. If you’re the ultra-sensitive type who is easily swayed by the strong emotions of others, do work on keeping your boundaries clear before opening yourself to an even stronger and more intense experience.
3. People with small children, or other full-time responsibilities that cannot be shirked. Being a horse can take up a sizeable chunk of your life. If you are needed on a moment’s notice by dependents whose care hangs on you and you aren’t home in your own body, it can cause problems. You might want to wait until some future date when you are no longer responsible for them and your time is your own. If the Gods are not going to let you off, you can pray to the Mother - that's the Big Mother whom all mother goddesses draw their sacredness from - and ask Her to intervene and give you space in which to raise your child. I did that, and it worked, although I paid for it later.
4. People with issues of mental illness that make their grip on reality tenuous at best and easily thrown off. This includes those with uncontrolled dissociative identity disorder (also called multiple personality disorder), where all of the individual may not be able to consent to the horsing, and where there is a higher likelihood of one "personality" taking on the archetype of the deity that sat next to it for a time, and believing that it is indeed that deity. Some shamans with excellent control over these disorders have been able to use them as tools to make possession easier, but that is advanced work.
5. People who are desperate for importance in their spiritual community, and think that this is a way to achieve attention and prestige. It's more like being the divine limo driver, actually. It's grunt work, and if you go into it with ego issues, the Gods who use you may find ways to slap you down....perhaps leaving you to clean up their divine messes. If you can't be humble about it, don't do it...and don't let your community give you lots of special head-pats for being the suit that the God wears, either. It encourages the wrong mindset.