Translation:Are you tired?
Why is 很 not necessary here before 累? I thought that 很 was necessary before adjectives in these kinds of description situations.
That is only a simplified way of explaining it. The rule is to enable the listener to perceive the magnitude of the adjective whenever that adjective refers to a progressive property. In a question and its direct response, such rule does not apply. The conversation can be:
For the first question both the question and answer does not require 很. For the second question, the issue in concern is how tired the listener is; the listener must answer with a magnitude of some kind, but you can see 2 of the sample replies I have given do not have 很 in it.