I have this problem at work. Sit and stare at my screen for an hour trying to make myself do something but as soon as someone else asks for my help I jump right on their thing... Sometimes of their thing is similar enough to mine I can trick myself into doing mine too but that doesn't always work.
I get 0 done without lists. People laugh about my lists, because every tiny detail has to be on it. So let's say I'm in the situation you described, and it's 10:30 am. What I'd tell myself is: There isn't even a list, so let's make a list, and if it's the last thing I'll do before lunch.
The list is quite often as detailed as:
decide which task / ticket to work on
ask coworker for advice what is suitable
assign myself to the task
read the task start to end
understand the task
reproduce the problem (if it's like a bug that needs fixing)
... and so on
Then, even in my worst state, I can tell myself: You can check off just the next item. That's not overwhelming, that's not too much.
Yeah I need this too! But for me a long list is in itself overwhelming. So I started to use blank cards (like those in hotels) and only put 3 todos on them with a whiteboard marker. I still have the long list somewhere on my pc but this way, I only ever see 3 calls to action. I tend to make them more specific on the card.
This also comes with the satisfaction of wiping away a task when it’s done (I hate a long list with striked through tasks, because I have to scan to find the remaining ones).