Bamber wouldn't be tired. The adreleline & thought of 435k would keep him going.
He did tell the police he was starving a few hours later. I'm not surprised.
Interestingly the police did not see any sign of particularly raised adrenaline but rather they reported he seemed mainly calm but emotional at times.
As far as we know he had not eaten much the evening before. In his words he had fallen asleep and woken suddenly to the phone call from his father which must have raised his adrenaline to some extent.
It's hardly a 'clue' of his guilt that by the morning he was suffering from shock and low blood sugar, causing him to have distended pupils and to feel 'starving'. Anyone would.
To say he had been 'sick on whisky' is far fetched, he had a mouthful of whisky that made him wretch, again that's not surprising, particularly if his blood sugar was low.
JB may be an amazing actor who knew exactly how to behave in such circumstances or he behaved in a way not unexpected by anyone in such circumstances.
At the time the police did not comment on any of his behaviour being unusual. It was only later after he became the suspect that some police, with hindsight claimed they had questioned some of his behaviour. Hindsight is a wonderful thing.
Sitting at a computer 30 odd years later picking out the points which backup your own arguments is a pretty wonderful thing as well.