A work day/week consists of two phases, which alternate more or less rapidly depending on the individual.*
There is the high-energy phase, in which one is Able To Do Many Things. Ironically, in this phase you are able to think up many more things than you can actually do before running out of energy, most of which are productive and helpful.
Then there is the phase you hit around three in the afternoon (and at various other times including, but not limited to, any time you have to read long articles written by someone who likes academic German syntax). In these off-peak times, not only can one not apply oneself to any of the obvious tasks at hand, one is seemingly incapable of thinking up any less difficult but still useful tasks.
This is where a pencil and paper come in handy. During peak times, I write down all of the handy ideas I’m having for later, so as (mostly) not to interrupt what I’m working on so successfully. Then during the off-peak times, I don’t have to think at all; just do the next thing on the list. Preferably one that doesn’t involve involved articles.
Panicking about giving a talk at a conference can be slotted in at any time, but is, in the interest of mental health, best done in brief intervals instead of sustained slogs.
So far, so good.
* If you have only one phase, with an Edison-style consistent and direct flow of energy, I’m not sure I will ever be able to understand you. Academics seem, by and large, to run on the Tesla model of alternating current.