its cold out there

yesterday I took out the mountain bike and road some trails. it was cold, 24*F. The first time pulling the rear brake I got 0 response (hydraulic discs). If i pumped the brake I would eventually get pressure. Could this be just that it was cold or do I have another issue going on? Maybe low fluid? air or moisture int he line? I’ve never serviced them so it could be time. I have no idea how to go about doing that.

My legs were sluggish, probably from lack of sleep and cold. My fingers were killing me half way thru from the cold, which is just about the time I blew out my front tire. I wasn’t about to sit there and try to swap out the tube so I just put air in it. It would last about a half mile until going flat again. Today its 18, I’ll probably just hide inside.