My piano lessons are a bit stressful but that is only because of ME not my teacher. It is just that when I have practised really hard and want sooo much to be able to play something right, or achieve great tone I get mad at myself when I can't do it at my lesson even though I've managed it at home.
My teacher is great and it is important to me that she sees that I've tried.
Her favourite phrase is "well there are some really nice things happening in that piece ........" which I know will always be followed by a "but let's just try and ..."
I have got tearful occassionally in lessons but not cos of her only cos I'm so cross at ME

Lucky for me I think she knows its a 'trait' in my character and not me being a baby. I wonder why I'm like this. It happens with schoolwork too when I really really want to get it all right and have tried super-hard and don't.