It has been a myth in our place (or perhaps in your place/country, too) that when a dog howls at the middle of the night and then act as if they are scared, there are bad ghosts or elements around. Is this true? If not, what could be the reason behind it?

I don't know? I've never heard that one before. My dog just recently started howling during the day and the night - I thought maybe because he was in heat.

I'd like to hear others thoughts on this as well.

My understanding is that dogs have hearing in frequencies well beyond the scope of humans. The low end of the range is similar (around 250 Hz ) but dogs hear noises up to 45 kHz, while humans only hear sounds up to about 23 kHz.

Because of this they are exposed to sounds that we simply are unaware of. These sounds could effect them the way sound does us possibly comforting, annoying or at times painful. Because of this extreme sensitivity they have a smaller dynamic range (the difference between comfort and painful levels) than humans do.

Howling may or may not be the result of pain and may simply be your dogs way of saying "Hey, get out of here" to whatever it is that he/she is experiencing.

Thanks for that, savegrey! You really are a genius in this forum and a great contribution. We learn a lot from your posts.
It is true, I have heard that, too, that dogs have good hearing frequency. In fact, most animals do and in the signs of danger, they are the ones which can sense right away, if there's a sound or vibration that goes with it, e.g., earthquakes, tsunamis.

Thanks

I personally wouldn't sleep at night if I thought my dog was seeing things I couldn't. My imagination is likely much more vivid than the reality of what he might be seeing in that scenario. Knowing howling is related to hearing helps me sleep better even if he doesn't....