I have only experienced Bipolar from my dad so please excuse me if I get this all completely wrong but I wanted to try and explain why borderlines are not diagnosed as Bipolar.
Emotions in both illnesses are of the extreme kind but they are different in the ways that:
Bipolar extreme emotions are generally up and down, with no inbetween (when uncontrolled).
With Borderline Personality Disorder, you may not know which emotion you’re feeling because you can experience many things at once. The change can be very quick from one to another. There isn’t really any kind of mania in BPD.
Bipolar moods are often due to chemical imbalances (with occasional triggers). This is why Bipolar is easier to treat with medication than BPD.
Borderline moods are (often) learned through upbringing and experience. A lack of a controlled home environment or unstable parents can often lead to an inability to understand an appropriate reaction to a situation. Dissapointment is a big factor in the big Borderline mood swings.
Bipolar lows come from the imbalances and are triggered by traumatic events which cause severe depression. They can’t always be explained.
Borderline lows sometimes have no cause, there is a general feeling of emptiness at all times.
Bipolar highs are often followed by delusional thinking such as feelings of grandeur and even beliefs of super human abilities which can lead to harmful things like over spending or promiscuity.
Borderline highs don’t often occur but when they do the feeling is very limited and doesn’t last. This is why people with BPD are known for addictions and potentially harmful activities such as spending a lot of money or promiscuity due to wanting that high again and again. It doesn’t have lasting effects.
Although both Bipolar and Borderline are often associated with the same potentially harmful activities, the reasoning is generally different. People with Bipolar do the harmful things because they feel high, like they can do anything. Whereas Borderlines are trying to create that high.
People with Bipolar are generally hospitalised due to harmful manic behaviour or depression.
People with Borderline personality disorder and generally hospitalised due to severe self harm or suicide attempts.
They can be very similar and can be diagnosed together but there are major differences between the two. I generally see Borderline as more of a natural reaction to traumatic events whereas Bipolar is more an inherited chemical illness that is often combined with trauma. Some people with Bipolar have the illness despite a “good” early life whereas people with Borderline have generally have some kind of trauma or abuse during childhood.
I know so many people who feel they would rather have anything but Borderline Personality Disorder due to the stigma surrounding it but seeing Bipolar in my father makes me most afraid of that illness. When I was diagnosed with Borderline Personality disorder my first thought was “I don’t have Bipolar, thank goodness” because to me anything other than Bipolar was better because of what I had already suffered with it. Please don’t feel offended, I know a lot of you who read this blog may have Bipolar but you will know more than anyone how hard it is. All mental illnesses are awful but when you’ve grown up with one that has taken someone special from you, you will always have that little spot in you that say, this one needs to be destroyed first.