Short sleep has a specific effect profile. Reaction time suffers a little, but the larger losses are in inhibition and risk evaluation: tired people take bigger risks, respond more strongly to rewards, and discount losses more. That is a precise description of a bad trading day.
The cruel part is that self-assessment degrades alongside performance, so the deficit is invisible from the inside. This is why a sleep field in a behaviour-journal is more useful than a subjective readiness rating.
Treat it as a risk parameter rather than a lifestyle matter. Under a defined threshold, trade smaller or not at all. Overnight sessions and early opens in distant time zones deserve a written rule, because that is exactly when the judgement to make one is missing.
Related: decision-fatigue, burnout, behaviour-journal, pre-market-routine