I am diagnosed with both. I experience severe depression that can last years. I also experience mania in that I all but stop sleeping, bounce off the walls and talk at an insane rate. I feel invincible. They are very distinct states that last a while.

Borderline causes me to flip emotions really fast. So I can be having the most amazing day ever and then be in the depths of dispair. I feel everything intensely. Every hurt is like being stabbed in the chest, happiness feels like the best day in the world and rage makes me homicidal. I think in black and white. Things are either good or bad. You're my friend or your not. I like it or I dont. I dont understand grey areas. I can be very manipulative and antagonistic. I fear abandonment and alternate between pushing people away and pulling them close. I get extremely paranoid and I also dissociate to where I feel like I'm watching myself. I'm extremely impulsive and react without thinking. I will decide something is a great idea based on my current emotion and do it.

Some of the overlaps with bipolar include self harm and suicidal ideation. The emotional instability is more rapid fire with BPD. So for me personally I'll get severe depression, but have moments where I feel amazing. I also find that medication helps manage bipolar. It got rid of my depression. But it doesnt do a lot for borderline.

The last time I was hospitalized the psychiatrist said I had borderline not bipolar. She put me on zoloft and I went hypomanic pretty much right away. I cant do antidepressants without a mood stabilizer. When she saw that she agreed with the bipolar diagnosis and added borderline as well.

Sorry for the novel. Hopefully some if it is of value.