I know there’s simple personality ticks, small things that maybe don’t have a lot of explanation to them that occur with us. So, I’m prepared if this is just an observation and doesn’t have a solid explanation… but… 
I notice that anytime I decide to tag along with someone for their errands, maybe go grab a bite to eat (family, generally) I always try to hint to the person tjay “I’ve got things to do later, so I have to be back after this” — to avoid being stuck and doing random spontaneous things. Now, I LIKE spontaneous acts, usually, but only on my accord. I do not like or even consider it spontaneous and fun when someone else thinks they can assume my time is theirs to take, and go do said spontaneous event that wasn’t originally planned. The reason I do this is because when I don’t, I feel so much agitation, displaced anger, physiological signs of stress like jaw clenched, bouncing leg. I genuinely feel “stuck.” And even when I do know the event we are going to, and I try to prepare for however long it’s suppose to be… sometimes I become immediately quiet, closed off and very clearly am “wrapping it up” for myself bc I’m simply ready to go. It feels like it keeps me from enjoying family time. I don’t know if this is an isolation thing I should combat, or if I should nurture it being that I have this insight about myself. What could it be from? For minimal background knowledge, I have BPD (you could say in high functioning but when you see me in “the act”c you’d see in really.. not. Definitely an every day struggle to not take things personally and be skillful, going against every natural urge I have), and I’ve completed 2 years of DBT therapy. I can walk the talk. Anyone have ideas? Thanks in advance