I have to second Mark in all he has said! I have had multiple impacts throughout the past 3 years, (2 work related and most recent a car accident). Each time it has been a harder, longer, more painful recovery.

I'm sure you have a great love for horses and for ridding. However, is it worth the risk of a lifetime of PCS? It's an individual decision that only you can make. However, you should know that doing so, even when you feel healed, makes a lifetime with this a possiblity.

As for trying to find milder exercises for now, consider your symptoms. If balance and vestibular problems are an issue, chose wisely! You don't want to accidently fall and hurt yourself more. The trick for me seems to be finding activities that don't up my heart rate. (Increase in heart rate for me= immediate return of symptoms, disabling me for the rest of the day). I have been mostly taking walks. (I used to do cardio and weights 45 minutes a day, and hate how lethargic and gross I feel... however pushing it is SO not worth how it makes me feel after!).

I think I may give swimming a try, just have to find a pool.

The best advice is to listen to your body. If the activity you chose makes you feel worse afterwards, you are slowing down your recovery and need to step back. This is NOT a situation of no pain, no gain...

Hope you can find something that works for you