I'm trying to model something, and failing miserably. So I'm going to try to articulate my vision, hoping for inspiration.
Imagine a large number of cars forever circling around a very large roundabout. Initially they are all going the same speed, and are evenly spaced. What happens if one car slows down temporarily? (I saw a Japanese(?) video of this somewhere.)
If the buffer zone between the cars is wide, and if each driver is flexible about the size of the buffer zone between him and the car in front, nothing much happens at all. There may be a small ripple in the flow, as following drivers slow down too, but the ripple will soon die out as each successive driver slows down a smaller amount than the driver immediately in front.
But if the buffer zone between cars is narrower, or if each driver is less flexible about the size of the buffer zone between him and the car in front, the ripple of slowing cars will spread to more cars, and will take longer to die out.
What would it take for the ripple to get bigger, and create a chain reaction? If the following car, having seen the driver in front slow down temporarily, decides he needs to keep a bigger buffer zone between him and the car in front, he will slow down temporarily by a greater amount than the car in front. The ripple spreads, and gets bigger as it spreads, until all the cars slow down. And there may be some cars that grind to a complete halt, temporarily, until the cars in front start moving again.
Money and cars are not exactly the same, so the analogy won't be perfect. But money does circulate around the Wicksellian roundabout, as one person buys from another, who buys from another, ... until the money comes back to the original person. And it is difficult to synchronise your spending and receipts of money exactly, so you keep a buffer stock of money, which means you don't spend the money immediately after you get it. The bigger the buffer zone gap between payments and receipts of money, the slower the velocity of circulation of money.
And if the buffer zone is small, or if each person is inflexible about the size of that buffer zone, a temporary delay in one person spending will create a ripple of delays that takes a longer time to die out.
And if observing that ripple causes people to want to increase the size of the buffer zone, and reduce velocity, the ripple will get bigger as it spreads. The whole economy slows down as V falls everywhere, unless the central bank increases M in proportion, to keep MV constant. That's a recession. And if some people stop buying altogether, while they wait for the person who buys from them to start buying, that's a liquidity crisis.
That's all. It's only an unclear Leijonhufvudian/monetarist vision, and not a model. My math probably isn't good enough to model it anyway. But if I could model it, I would get a simple model of both liquidity crises and recessions, using just MV=PT and an equation for V.