My mother has an occasional habit of giving me advice as if I were still a child. This is especially frustrating since in many ways I am better at dealing with the outside world than she is.
But I guess it is often hard for parents to accept that their children are adults. Also, I suppose some people may think that treating you like a child is somehow comforting to you. I can really understand your distaste for your mother's patronizing tone. There have been times when I have wanted to hang up on my mother too.
I suppose the mature approach might be to try to discuss with your mother how her tone makes you feel, but that doesn't necessarily mean that you will be able to get through to her. She might even say she understands and will try not to do it again, but don't be surprised if the next time a similar situation occurs, she resorts back to that behavior.
There is nothing immature about saying you want to climb under the cover and never come out. It isn't even immature to climb into bed and hide for a while. It is a problem if you don't come out, but I think it's fairly clear you were expressing yourself in figurative terms.
Anyway, my guess is your mother is trying to be helpful in the way she feels is right. It just isn't right for you. Sometimes you just have to let your parents say what they need to say so they feel better and then you should turn to someone else for comforting that will actually help you.
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Never let the weeds get higher than the garden,
Always keep a sapphire in your mind.
(Tom Waits "Get Behind the Mule")