Having worked with the public for the past 40+ years, mindfulness, self-discipline, self-regulation is something that must be consciously applied. It's very much like masking. At work, for example, you can't be "yourself" because you are a representative of the company, and it's when the employee "breaks" that the customer gets upset, wants to complain, and may ultimately lead to that employee being fired. Another way to think of it is that it is very much part of a "cultural-social experience". We behave a certain way based upon the expectations of that environment. In specific circumstances, yes, it can be mentally exhausting.
Where I think that autistics can have some disadvantage or difficulty here is that, (1) depending upon your mental maturity, your intellect, your upbringing, and your autism variant, there can be a tendency to operate on an emotional level, which is the antithesis of operating on a logical level, (2) you might not be cueing in on the cultural and social aspects of hierarchy and "your place or role" in a given situation, (3) if your excitatory-to-inhibitory neurotransmitters are in a predominantly excitatory imbalance, you are more likely to express "stimming behaviors", frustration, anger, and emotional outbursts when others or the situation demand rapid flipping from one task to another, multiple people trying to talk to you, disruptions in the flow of thought, etc., and (4) most of us are trying to mask our autism in public anyways.
It is not uncommon, at certain points in our lives that multiple situations arise that ultimately add one stress upon another upon another, and finally, our brains become so exhausted that our abilities to "maintain composure" begin to fail, our abilities to think logically fail and we become more emotional, our sensory issues come forward, our abilities to mask fail, and we "become more autistic".
It's a miserable feeling, this "autistic burnout". This hyperawareness of our condition can lead to further depression, self-deprecation, jealousy, envy, anger, frustration, suicidal ideation, "I'm such a failure.", "I will never have,...", the whole spiraling down. We see a lot of threads like this on the forums when people get into this mode of thought and I find myself not replying now-a-days because I know now that the more you talk about it, the more the situation becomes amplified. This idea that we should talk about our problems is, as I am discovering, counterintuitive. For many, it just makes it all worse. I can be empathetic to the situation, but expressing that empathy, "I am so sorry for,..." amplifies it. If you try to give helpful suggestions, then sometimes the person is just looking for emotional support, and is not looking for someone to "fix the situation". It's a minefield. As they say, "Damned if you do, damned if you don't." or "The road to Hell is paved with good intentions."
You really have to be selective and think about how ou are giving support to someone.