And with the greatest respect your fellow poster's conjecture was simply another attempt to explain away the fact that the McCanns, when they had concerns that their children had been sedated by an unknown, potentially lethal drug, did nothing.
In your opinion. IMO the fact they brought it up with the FLO's on the 5th was because the concerns they mentioned on the 3rd had not resulted in any feedback from the PJ. I also believe the language barrier really worked against them in those first few hours.
I don't believe Kate thought they had been sedated with a potentially lethal drug - neither did any of the other doctors - otherwise they would have taken more drastic action. The fact that the twins were sleeping soundly was normal for them anyway - IOW they were not light sleepers - which could explain why they didn't wake up. That would influence the level of her concern IMO.
Add to that the terrible state of abject terror and anxiety both parents were in - worsening by the minute, then any idea that they should have been thinking calmly and logically - believing as they did that their daughter had just been abducted, is so unrealistic it's off the scale. They would be consumed with fear for their missing daughter. No parent could think straight in those horrendous circumstances. Their heads would be all over the place.
On the other hand there were policemen there who did find it strange that the twins didn't wake up. Those officers were not in a state of shock and anxiety and IMO should have reported their observations to their superiors asap - who may have suggested to the parents that immediate testing was appropriate.
The fact that there were no formal instructions or guidance available to the police on what to do in these circumstances was unfortunate from all points of view IMO. I sincerely hope that state of affairs has since been addressed.
AIMHO