Created a throwaway to say that as someone being treated for ADHD as of recently, 100% this. Every day at work for years had been doing exactly what the GP describes. If I'm really interested in the work, I'm all in and focused. But when I'm not, I push off every task that can be pushed off as far as possible. And the overwhelming majority of the time, it's the latter. To the point that I've sat at my desk quietly questioning my career choice dozens of times.
Please look into this, GP.