This Tisha B'av morning I was at the Kotel for shachrit, and I noticed a whole bunch of people sleeping there. I'm not talking about people who nodded off during slichot due to low blood sugar, I'm talking about dozens and dozens of people who clearly spent the night there. Many were stretched out on blankets or sleeping mats. (I didn't see any pillows). A Jpost article has a picture if you want to see, and there were also mentions of the practice here, here, and here.
However, I cannot find anything about the origins of this practice. I know there is a tradition to sleep on a hard floor on Tisha B'av (which the kotel provides), but I feel like there has to be more to it than that. Does anyone know when and how this started? Was it ever done pre-1948 or is it a post-1967 phenomena?