My biggest fear of a disability is of any one that can make you go insane and lose your mind. Ideas are your most powerful tools after all. You cannot innovate or progress without cognition and internalization. Without your hands and feet you are still a full person, capable of achieving and dreaming. Without your senses you are a bag of bones and meat, flailing around and being a burden to others. You are still a human, but devoid of means to actually act like one. I just don't want to become useless with my mind before anything else in my body gives way.
It is crucial to try and remain sane at all times. Don't exaust your brain, don't put it in too much of a stress, but don't let it completely relax either. Lazy brain is no good at getting back running again, when it becomes important. Reading is good for that, but preferably choose non-fiction. Reading something technical can wake a curious bug in your mind and allow you to chew on it for some time. It's like a good LEGO set. You buy it to build something predetermined, but what it actually does for you is give you tools to create something original. You simply need to try and put two bricks in a way you were not guided to do. Just read something in a field that interests you and the same thing is going to happen in your brain.
But just as with your body you need to ration your consumption of junk. You can allow yourself some junk from time to time, but just because you are hungry for new information all the time you don't need to actually start consuming whatever information is easily accessible to you. Social networks and tabloids will fill your mind with useless crap and you will not have enough mental capacity to produce new ideas. If you are starving for some new perspective, meet people and talk to them. You get better brain activity from drinking with someone than from swiping down on your Instagram feed. (But drink responsibly, please!)
In minutes of calm and lonelyness your best honing tools are self-reflection and internalization. Just dig inside and look for clues in your behaviour, that can tell you more about yourself. It can give you insight on a problem you have been struggling with, and it can also show you a problem you were not aware of. Like checking yourself for new lumps in unexpected places you should check your brain and mental state as well. Why are you down all the time? Is it just weather, or is there something else in your life that subconsciously affects you? Get to the root, and then sit on it for a while. You don't need to change something immediately. After all, you can be wrong. Live with this idea for some time, get accustomed. Then start making changes to your life for a positive outcome.
But don't sit on your ass for too long. Man, I need to get into a productive state of mind sooner rather than later.