I see you are located in the UK...here in the USA it may be a bit different. example here we no longer have a diagnosis called complex PTSD. most if not all our diagnostics for mental disorders now also include a criteria that states the problem can not be better explained by another mental disorder.

what does that mean here in the USA....many people who have been diagnosed with 2 or more mental disorder end up getting diagnosed with the one mental disorder that best fits their problems, when more than one mental disorder label is used its because of the symptoms\diagnostics that do not cross over into the other existing mental disorder.

example your post translated into american diagnostics..

your post.....Yes I'm aware we are hypervigellent but we have a difficult time working out if we/i are over reacting to many things, situations. There has been a upset with someone I know, it's been difficult trying to work out if I have over reacted, I don't think I have.

here in america what you posted would be PTSD symptoms.

borderline personality disorder symptoms would be things like impairments in self functioning( having trouble with caring for your basic needs like hygiene, cooking, wearing appropriate clothing that the weather calls for, ...) poor self esteem, poor self image, unstable goals\making plans then not able to follow through, trouble recognizing feelings\showing empathy, intense relationships,....

see what I mean about america is a bit different than the UK where diagnosing mental disorders is involved.

my suggestion is go according to what ever your own treatment providers said you have and the treatment plans they have set for you, they are the ones diagnosing and treating you there in the UK.