Some tasks fit into an awkward sort of "squeezed middle". If something is quick and simple to do and doesn't disrupt the rest of life too much, you might as well get on and do it. Urgent tasks are usually not too hard to remember to do and to get on with, and long tasks are readily handled by putting the into your diary. In the middle are tasks that you need to do, but can't do easily find time to get around to. So they build up. That in itself starts to cause a problem - it's much more bother to have twelve 10-minute tasks than one 2-hour task. That's because there is an invisble 13th task ("keep track of all of the 12 tasks"). The mental pressure of feeling there is a lot to do can be very unpleasant - even if it's "a large number of tasks to think about" as opposed to "many hours of work"
Somebody once told me that old-time mainframe computers had a problem like this. They had to cope with prioritizing tasks for many different users. So the computer would run a program which would decide the best order in which to do the tasks. But of course that choosing program itself needed some of the computer's resources. As more and more tasks piled up in the queue, the computer could get stuck allocating more and more of its resources into deciding what to do. Endgame is that ALL the computer's resoures are going into trying to decide what to do next, and the computer has had a sort of digital nervous breakdown. The number of tasks that would cause this was known as the "thrashing number", I was told. To prevent this from actually happening, the computer would be programmed to change its behaviour as it felt the thrashing number approach - move from doing the tasks in the most efficient order to just doing them: get the length of the queue down any old how, until the situation improves enough to think about efficiency instead of survival again.
Something similar can help for people too, I think. If you normally take some care over prioritizing but have ended up "thrashing", it can be helpful just to let that go sometimes and reduce the queue: do the thing that is bothering you first. Or, do the small things first; or just do things in any order to get life more simple again so you can think straight.
To avoid things getting that bad, it's helpful to set aside a fairly regular "thrashing hour" in which you work through as many of those inconvenient-sized tasks as you can. OK, it's something of a misnomer as the idea is to prevent the kind of behaviour which was "thrashing" for a computer. But "2pm Friday - thrashing hour" is such a satisfying thing to write in the diary.