Weird. Yawning means tired? Okay, I'll try that... Health Icon flashing = simple screen glitch. Nothing sinister. Stuff like that happens all the time!
Does it ever seem to you that your Tamagotchi stops doing something (yawning etc) as soon as you look at it? Mine does that. It's really spooky. Sometimes when I enter the Games Icon, a "sun" flashes briefly on the screen (like a "Happy Sun").