No overdose is meant, sometimes the body reacts the opposite, this is why only doctors should administrate sedatives. The question is justified by the fact both twins were reported as sleeping amazingly among noises, voices, screams and checked by their mother many times, showing she realized her babies weren't therefore sleeping "normally".
Who drugged the twins and why ?
Some little ones are amazing what they will sleep thru. Here we do not know how much of the noise actually surrounded them, Doors can be shut to compartmentalize sound. Kate was bound to be over anxious about them and would keep an extra eye on them, by frequent checks.
Personally, I have felt all three children had something slipped into their teatime drinks .... or possibly were given sweeties that were some sport of drugs. This is the third time I have said this, but I will say it again. Madeleine was sooooo tired at 5.35ish that they had to carry her back to the apartment. That is very early considering that IIRC their bedtime was normally 7.45
Also each evening, the pattern had been to bath the children and get them in their jammies, then to take them to join up with the other children for a play on the climbing frame, slide etc for a while before going to bed. That night they were too tired to go and play.
All these things indicate the likelyhood that some sort of drug was administered to them at Teatime, with possibly a double dose for Madeleine
OMO, but what do you think about it Anne? Seems you know quite a lot about drugs and sedatives.
Could what I am saying make sense?