Last couple of nights temps were predicted to be in the mid 20's. I decided to try a backyard hang primarily to try out a top insulation configuration that would be multi-use. I combined a JRB Stealth TQ (45º) over a GoLite Ultra 20 (35-40º for me) with the idea that the Stealth would double as my camp jacket. I had a WB Winter Yeti UQ and a GG Sleep Lite pad in the footbox of the GoLite to insulate my feet. I wore a light weight set of Merino long johns, down socks, a merino Buff and a Black Rock down beanie. Now I have spent many nights on the trail with a 3-season Yeti and was fine down to the low 30's. Well this time at around 1:30 in the morning (with the temp only 31.8º) I woke with the dreaded CBS, actually the cold back syndrome. I got up and sandwiched a summer LeighLo's UQ between the Yeti and the hammock and it solved the problem. But now that has just added weight that I was trying to eliminate. I'm no Noob but I can not understand what has happened.