Last night, I fell asleep watching a YouTube video on my Galaxy s5 (Android version 4.4.4). I woke up hours later to the same video still playing, and I went to grab my phone and it was EXTREMELY hot, still cool enough for me to touch it though, so I checked the CPU temp and it said 149°. I literally thought my phone was going to explode. I quickly shut the phone down and took the battery out and let it cool down until the next morning, and I haven't had this problem since. I was wondering if anyone had any explanation and/or ways to prevent that from happening in the future.