I have a fluctuating personality, due to my (suspected) BPD. It may not be noticeable to everyone but I can act very different at times. This is due to my unstable sense of self, I often don't know who I really am. Unstable self of sense is extremely common in people with BPD (it being on the diagnostic criteria).
My personality often changes between
hyper, loud, and annoying
calm, caring, and formal
emotionally unstable, impulsive, and mean
shy, reserved, and childish.
Although, I often tend to act the same over text to not cause others confusion or worry.
Do not confuse this with DID, I am one person and I hold all memories (despite being extremely forgetful..).