alright so it is my first time flying the a321 in 5 months, but when I was doing London Heathrow to Dublin the plane kept bobbing up and down. I was powerless for a few minutes but managed to gain control later. The same issue popped up again so any help would be great.
On takeoff, winds were 0 and my VS was 4000
Speed: M.85 (maybe why this happened)
About at the end of the flight, I intentionally sped up trying to get to Dublin faster