I've ridden many hours solo. I also have friends who have ridden alone ALOT.
Everybody gets hurt at sometime if you play with horses long enough. The trick is to be prepared, so that if something happens you can get help or take care of yourself until help can arrive.
I'll give you a couple of stories, maybe you can learn a few things from them
I was ponying a young two year old gelding. I was riding a seasoned gelding. While stopped. I had tied the seasoned gelding up. The young horse was loose. Both horses were saddled. Teaching the young gelding to carry an empty saddle. The young horse came seeking a treat, or some attention. In doing so he stuck his neck under the neck of the older gelding. He caught the older gelding reins on his saddle horn. I jumped in quickly to try and untangle them. The older gelding feeling the pull on the reins, moved to try and release the pressure. the colt feeling the tug on the saddle horn, panic and jumped forward. He head butted me square int he chest, knocking me to the ground. I blew out all the ligiments and tendons in my wrist. I had to climb into the saddle, ride two hours ponying a young horse with a wrist that was in serious pain. I ended up in surgery, had a 4 pins and cast for 8 weeks. Lesson learned. 1. Let the horses break the reins, step back out of the way. 2. Carry some string or other materials to repair broken reins.
Story number 2 was a friend, He went out for afternoon ride in late February. It was a nice day, He planned for two hours in the afternoon sun. During the ride, his horse slipped in some mud and went down. He broke his pelvis and ruptured his bladder. He lay in the mud for 13 hours unable to get to his feet. His wife came home from work and finally noticed he wasn't home. She finally called the sheriff around 10pm, They searched several places that they knew he liked to ride. Around 2am, they found him. Around 4 am they got him airlifted to a hospital. He spent 6 months in recovery. Lessons Learned. Tell somebody where you are going and when they should expect you back. Carry appropriate clothing for the season. My friend lay int he mud in 16* temps in a single long sleeve shirt because he had no jacket or extra clothing with him. Where he was ridding, a cell phone didn't have service. But if you are in an area with service, Carry a cell phone on your person. Remember, he couldn't stand up, so a cell phone in a saddle bag was still out of reach.
Story #3. Another friend is a horse trainer. He spends 8 hours a day riding horses. Usually solo. He was out working a clients horse on the trails. The horse tripped and went down. It shattered his leg when the horse landed on it. He also had to get back on the horse and ride several miles back to his home. Lesson Learned. You need to practice mounting and dismounting with injuries. Sometimes you just have to cowboy up and find a way home. In mountainous territory, riding the horse may be easier than trying to walk through rough country. Can you mount your horse with one hand? Can you mount your horse with one leg?
Now any one of these accidents could have happened while riding with others or by yourself. But if they happen when you are alone, you must deal with the problem.
I always carry water, some granola bars, matches, a space blanket, depending on the season/location a rain jacket. If I get wet, I can start a fire. If I get stranded over night, I can roll up in the space blanket or I can use it for shelter from the wind or weather.
I really enjoy a day out ridding my horse, they learn to trust me instead of using the herd for security. Don't be afraid to get out and enjoy the experience. But be reasonible and plan for unexpected events.