Thanks to everyone for your replies. Looks like this non insulated air pad is the problem. I figured the tyvek would be enough but I guess I learned the hard way. I did drink a litter of water before I started the trip and close to a litter during the trip along with some electrolyte mix, had dinner as well. Felt like I was coming down with something but was fine the next day. It was only a 5 mile hike but the elevation along with the pad were more then likely the culprit. Thanks everyone for your help.. Stay warm..