Best way to know if you're in a simulation is to observe when it glitches (in a way that can't be explained by a glitch in the sub-simulation that is human perception).

You and several complete strangers see someone floating in the air without any technological support, assuming y'all haven't been poisoned in a similar way and are hallucinating, either a) there's some support you don't know how to look for, b) there's a condition of reality that hasn't been accounted for in the study of physics yet, or c) the rule set just straight broke somehow.

I don't think anyone has totally eliminated glitches in the human or an incomplete understanding of physics to really support a 'we live in a simulation' explanation for strange phenomena, at least not yet.