PD is a complex creature and difficult to understand. One way to overcome this problem is by using analogies to make it comprehensible. If a picture is worth a thousand words, then a good analogy is just as valuable.
One major feature of YOPD is the struggle to maintain homeostasis, or balance, in the mind and body. Like Goldilocks, one bowl of soup is too hot, one is too cold, but that one that is just right is what we are looking for. Constantly. One does not achieve balance and then take the day off. The pursuit of health, of homeostasis, in a sense IS living.
A healthy person is like a spinning top. Perhaps you remember playing with these as a child. One would wind a string about the top and, with practice, deftly flick the wrist while holding the end of the string. If all went well. the unwinding string imparted a brisk spin to the toy which then settled into a magical stability.
Like the top, we are born with a certain amount of “spin”. If you nudge a spinning top, it resists falling over and does so in direct relationship to the amount of spin. It will wobble slightly and then right itself. However, repeated nudges or single ones of larger magnitude produce greater wobble and more energy is drained from the system. Eventually, time takes its toll and the lovely order of spin dissolves into an undignified collapse.
That is the way our own bodies behave and this system for maintaining stability grows increasingly “dysregulated” in YOPD.