Question

But I saw this sentence: I wake up three times in the night. If this sentense is correct, I think it means general night instead of a special night. What do you think?

Answer 1

at night is general, in the night marks a specific night, hence the usage of 'the'.

Answer 2

I think it's safer to use "at night"

But you might want to check this out http://english.stackexchange.com/questions/121858/at-night-or-in-the-night

Answer 3

Hi, my teacher said if you do it regularly, you will use "at night", however, it just happens sometimes, use "in the night"