A mind is a structure for processing memory and sensory information.
All the sensory information it processes has been preprocessed by the body and put into the categories: Irrelevant, Um-Hmm, Maybe, Noted and This! Everything except This is kept out of your conscious attention along with all the other things you’re ignoring. If those things are important or ongoing they’re stored with a pattern of physical tension because nothing says Avoidance like squicky bowels.
Mind uses memory and combines it in new and interesting ways; the imagination. This is called thinking, if you are consciously doing it on purpose. If you are not doing it on purpose it’s called crazy. The mind uses memory and imagination to generate the psychological structure of a person, their personality and a lot of reasons why coffee and the internet are a great way of passing the time before mortality takes its inevitable toll.
If the mind is busy your awareness is limited to whatever it’s doing. You won’t notice nearly anything else unless someone sets off a firecracker. In this way if you are always busy everything in existence will calmly pass you by.
If you let your imagination run out of control in the endless interplay of possibilities between past and future – that is, if you have any inner experience that you don’t like of any kind at all which isn’t obviously caused by hangover related issues and other effluvia of the physical realm – it’s time to rein that sucker in.
How to Rein That Sucker In: practice. Like a toddler on sugar the thoughts never stop, but you can ignore them and wander off and put your focus on something else. After you get good at this you can turn your mind to your own uses and then ignore it. On its own it will just generate garbage in a constant narrative with varying connection strength to any actual reality.
It doesn’t matter what the mind does as long as you don’t mistake the stories it’s making for actual things. Sadly, anything you consider seriously has a way of quickly leaping into Actual Thingness so be on the lookout for that feature. By all means have fun with imaginary things but don’t get them confused with Actual Things. I think this is the basis of the contempt some people have for fantastic fiction but those people have usually failed to notice that their consensus reality including all social and cultural identities is entirely fictional. It’s just much less fantastically fun than the things I like.
On the downside of this sanity: the more sane (able to dip in and out of Mind at will) I got the less I was able to experience the thrilling possibilities of all kinds of weird shit that I thought at one point might be real and although that was great because I was no longer terrified/worried/constantly churning pointless things it was also a bit sad, like something had died.