Hey Blue_Bird, I'm so sorry you're feeling this way. You do try incredibly hard to be mindful of your thoughts and emotions. It can be very hard to get there and stay there when you have other thoughts affecting you at the same time. I think a discussion with your sister sounds like a wonderful plan.

In my mind positivity and negativity are equal opposites on a spectrum. Traveling from one to another can occur in several ways. Sometimes I can jump from one to the other with a little effort on my part. However, sometimes I just feel stuck and I stay in the same place for a while. Whether it is positive or negative, too much of either has an effect on me of imbalance. At these times I find it easier to create movement if I attempt my goal by making incremental changes. If I were in a dark place I might first seek slightly less dark. Next, I might lighten things up a bit more. After that, I'd try to achieve neutrality. From there, I can gently start working the positive self talk and thoughts back in that my mind would have instantly rejected if I tried them when I was too far down.

If one was in a self hate mode this might look something like...
Self hate -> Self pity -> Self acceptance -> Self forgiveness -> Self love

If I were in an unhealthy narcissistic Self love state I might go the other way and forgive myself and then accept myself. I'd skip the last two steps in that case becsuse the goal at that point would be to experience balance.

This may not resonate or be feasible for you at this time. I wanted to toss it out in case it helps to make a seemingly impossible journey feel slightly less impossible. Much love to you. We're all here should you need us.