You certainly are not the only one who overthinks & end up with a mind overfull so no wonder it feels all jumbled up!
It's like reading about myself - I also tend to fixate on something and obsess till it's done - may be a good thing, or perhaps not?
But trying to compartmentalise stuff - live in the moment and just do what you have to do today. Always remember to take things step by step, you can after all only do one thing at a time - do not over-multitask! That's also not so good.
By the way, my friend is proving the doctors wrong - a major turnaround in her condition - so looks like she's going to have one heck of a story to tell one day! She's literally come back from death!
And always remember to keep on smiling - you should check out a post by a lady called @zen-art about smiling, you will love it :):)