Imagine this, instead:
The scene starts out as normal, we are asleep, but restless, and as Astarion creeps on us suddenly your character wakes - Now, the scene dims slightly, the action slows to a halt just on the cusp of movement taking place; we've awoken, but we haven't reacted yet. HERE, it gives us out first scene dialogue choice - and it's a choice of a few different decisive actions; maybe you freeze up, maybe you grab a weapon, or prepare to cast a spell, maybe you try to back away, maybe you shout - only once you choose, does the scene play forward, to the point of dialogue (or murder as the case may be).
In this scenario, it's mechanically no different than having your character react first, then give dialogue options for you to define your reaction - either way, they will have to design a handful of different scene choreographies for the transition between waking and talking. The main difference is that if they let you decide how you're reacting initially before showing it, then they aren't violating your character by having them act in a decisive, specific way before giving you any input on the matter.
It's perfectly okay to have the Pc react in minor or non-committal ways during scenes, but actions such as grabbing weapons and threatening others are decisive, characterising actions, and they should never be taken by the player character in cutscenes without actual player input on the issue.
