When I an tired, the first thing to indicated this seems to be speech. Certain long callsigns with too many zero's or tongue tied letters together can give me issues - generally ending up as a mumble - which is frustrating as I take pride in complying with good form when it comes to RT. I have tried getting wired on caffine, slouching with the chair reclined, speaking fast and slow but unfortunately a good nights sleep isn't always possible as you all are too aware.