Security Camera Video Fades from Bright, halfway to black

Hi all! I've got a weird dilemma with my security camera video. When I switch to the input where the camera video is located, the picture is bright and clear, but then slowly fades darker and darker until it is about halfway to completely dark. If I switch to another input, say where the cable is, then immediately switch back to the camera input, the process begins all over again. My connections are cameras ->DVR, DVR ->TV. The DVR to TV connection is with a HDMI cable. I was wondering if anyone else has come across something like this, or have heard of anything like this before. Thanks!