My Panasonic TV switches from Netflix or DTV to HDMI3 without warning

My Panasonic TV switches from Netflix or DTV to HDMI3 without warning

Today my Panasonic TH-L42ET60A TV began switching from Netflix or DTV to HMI3 without warning. I have to select Netflix or the normal TV and start from scratch. This happens every 20 to 30 minutes. What should I do?

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