[johnfuller]

I think another item to add to this is that some days that 4 hour day is going to be your ceiling and anything which creates yet more cognitive exhaustion is going to erode that further. For example, serious stress from having to hit a deadline or being overloaded could bust that 4 hours worth of reserves down to 2 or 3. If you try to force it, you might just end up sitting at your workstation all day idling at brainless tasks such as browsing the internet or half attempting to create some sort of structure out of the mess of the task list your clients have sent you.

It's interesting that we see so many articles posted on hacker news on how to be more productive, beat procrastination and be more motivated when really this article the OP posted explains it all. In most cases you probably don't have a problem with procrastination and motivation, it's simply that you are over-extending yourself. Cut back your commitments and you fix your problem.