My wrist sensor unexpectedly jumps my heart rate to double my real heart rate, especially when I lay down to sleep. It stays high without explanation until I force my chest strap HRM to send actual Heart rate data, then it seems to reset to normal rates. I have had reasonably reliable heart rate data for several years and this just started on May 12 and has been persistent since. I have verified my actual heart rate is about 1/2 of what the wrist sensor says. I have tried repositioning the watch, cleaning, restarting. No real difference. Is this an update glich? I have a forerunner 945.