Feel free to use this answer with your boss as you practise taking shorter breaks more frequently.

You need me to be more responsive, but when I'm deep in a long-running task juggling a lot of little things in my head, it's hard for me to surface for air, evaluate whether I need to respond to your request right now, then drop what I'm doing to help you. That's why I've started training myself to take more frequent breaks. It encourages me to get stuff out of my head from time to time. As I practise this and improve at it, I'll be able to get everything out of my head in less than a minute when you really need me. I'll be able to focus on what you need to me do while I'm doing that without worrying that I've lost crucial information to get back to what I'm doing now. So if you bear with me while I'm practising taking breaks, then I'll be more responsive to you when you need me, I'll focus better on the work you need me to do at that time, and I won't need long to get back into the work I was doing when you interrupted me. We all win.