The fact that you're concerned about this speaks volumes.
My mum was very mercurial (I'm now sure she is bipolar) and her emotions were often very big, very intense, and very obvious to me. But it was the subtleties, too – I learned to read her face and her energy when I was very young, and most of my childhood was defined by trying to level her out – being funny and cheerful to stop her from being sad, or walking on eggshells to stop her exploding.
Children are naturally very ego-centric, in that they assume their main caregiver's emotions are because of them, so I internalised a lot and grew up thinking it was my fault she was so upset all the time. It's only recently, through a lot of therapy, that I'm starting to understand that I'm not a bad person, and be able to separate my sense of self from hers.
I now don't have a relationship with her – partly because of this, but for a whole host of other reasons, too.
Looking back now, with an adult's mind, I wish she had sought out help for the things she was dealing with, for her sake as well as for mine. I have huge compassion for all she was going through – it must have been so hard for her – and I wish she had cared enough about herself to address what she was experiencing.
And I wish she had been able to work on the 'repair' side of things.
So much of a healthy relationship isn't about everything going smoothly all the time – it's being able to have difficult moments and then come back to do the 'repair work' of apologising, acknowledging responsibility, and doing better next time. My mother was incapable of that – and still is – and it would have made the world of difference.