Disassociated mechanic is one where the decisions made by the character and decisions made by the player are not associated. I find this useful descriptor. It of course is not binary, the association may be weak or vague, or completely non-existent. But the concept is coherent enough to have use.
So, Alertness(1) is dissociated. Second Wind(2) is dissociated. Using a hit die during a rest(3) is dissociated. Hitpoints(4) are dissociated. Extra attack(5) is dissociated. Sneak attack(6) is dissociated. All of these are dissociated. Is it useful to you to appreciate this, and what steps might you take to address your dislike of these mechanics?
1. you cannot be surprised. No one wants to be surprise. The PC isn't choosing to not be surprised. Actual fiction doesn't matter here at all, either.
2. what is the PC doing here that grants hp back? Why can't the do it whenever? Why is this only a fighter ability?
3. What is the PC doing here that grants HP? Why can't they do that anytime they want without limit?
4. I mean, hitpoints, right? The easiest here is that the PC isn't attacking the enemy to remove some ablative plot armor, but to injure, maim, or kill. The result of "no fictional change" doesn't really track.
5. The PC choosing to go all out looks different at certain only mechanical breakpoints. The reasons that classes other than fighter never get more than one of these, or even none of these (most common) has no fictional basis that makes sense. It's a purely mechanic differentiation to allow fighters to not completely suck due to no magic.
6. Sneak attack has the same problems extra attack does -- why not let everyone do this?