Before I answer that one, let me address the question I know is on your mind: How the heck do you pronounce dysdiadochokinesia??? dys·di·ad·o·cho·ki·ne·sia. Don't worry, I still can't say it and I don't know if I really need to know how to say it. It doesn't sound like my computer's narrator can say it either! Try it for some fun! So yeah, let's just focus on what it is. Dysdiadochokinesia is the inability to produce rapidly alternating movements or rapid repetitive movements. This is the result of a lesion in the cerebellum which among other things controls skilled motor activity (such as playing the piano), coordination, and balance.
A common example (and where you might have noticed that you have this) of an inability to produce rapid repetitive movement is the inability to produce a smooth beat while tapping your foot on the floor. You want to produce "tap, tap, tap, tap" as you raise your toes up and down while keeping your heel on the floor. Instead you get "tap, pause, tap-tap, pause, tap" which maintains no rhythm what so ever.
An example of an inability to produce rapidly alternating movement would be the inability to (let's say),slap your thighs with the palms of your hands, then quickly flip your hands over to slap your thighs with the top side of your hands and repeat this movement for at least 10 seconds. It should be a smooth motion but instead it's a sloppy, limp, movement.
I know I had this symptom around the time I was in the physical rehabilitation hospital in 2012. My hands were pretty limp so it was hard to do any of the alternating hand stuff at first but for the longest time I could not continuously tap my foot. Once my hands improved I know I had a hard time keeping a beat going (on a table with my hands or fingers), it was erratically uncoordinated. Over time it did get better and now I have no problems with rapidly alternating movements but my feet are still a little slow with the tapping so I suppose I will have to let my lifelong dream of playing double bass drums in a death metal band go.