A whole chapter of flashbacks?

In my story, I want to give a look back into the past, which is so important to what's going on in the present time in the book. I'm kind of in a serious/somber part of the story; would it be too random or inappropriate to do a whole chapter of a flashback? Also, my writing teacher said if you explain everything, the story loses interest; though I'm not giving away anything for the future, would it be bad to tell something the reader would naturally be curious about, though it has no immediate significance? Sorry if this is confusing; thanks for any help.