Something has jumped into my head and im going to throw it out to you... have you been questioned/assessed for Bi-Polar Disorder? From the way you post, it sounds like your mood goes up and down like a yoyo and when your in a good mood, your in a great mood and when your in a low mood, your in a really low mood. Might be something to consider.
Back to the problem in hand... sounds like a communication problem to me. Are you able to sit down with your mum and have an adult conversation about this? To a certain extent I agree with your mum since I dont think that sugar coating everything for people is a good think because it gives them a false perspective but there is a time and a place for honesty and tactfulness is always a good skill to learn. Could you talk to your mum about this?
Its nothing to be embrrased about... communication seems to be a dying art-form these days. There are loads of people who cant do it or feel uncomfortable doing it. The good thing is that you are prepared to try and learn... and the only real way to do that is to practice.
Before you start the conversation, you need to pick a good time and have a list of things you want to discuss. Starting this after your mum has had a row on the phone to the gas board is not a smart move! If it helps you remember, write down the things you want to talk about. I would start the conversation by saying something like "Mum, I need to have a conversation with you but I need it to be honest and not end in a row..." If you get upset, its OK to cry. Its not a sign of weakness, just an expression of emotion. As for a productive pace, that is largely dependent on you. If it fels comfortable to you then its probably right. Long drawn out silences are not good. If you get big gaps in speech, change the subject... it probably means that youv'e reached the end of the conversation on that topic unless you have something specific you want to address. Its always nice to end the conversation with a thank-you and a hug. After all, you have both helped each other and its nice to show your gratitude and also to show that you dont hate her for being honest and saying something that upset you.
All the best