I've interacted with a number of different sleep labs (Germany and UK). All physicians I've spoken to are well aware of the fact, however, the effect size of wh

I've interacted with a number of different sleep labs (Germany and UK). All physicians I've spoken to are well aware of the fact, however, the effect size of what they are typically looking for is greater than this 1st night effect. E.g. if you have sleep apnea it will (very likely) show up on the first night already. If your condition is more subtle (e.g. sleepwalking) they will already book you for two nights. In addition, there is a counter-effect where people are struggling for years with their condition and being in a sleep lab brings some form of 'being taken serious'.