Not sure he was sleepy. Someone was trying to kill him.
He was still pretty mobile when on the stairs & in the early stages of the kitchen fight. As the kitchen crime scene shows. The fear & adrelaline of the situation negated the pain of the 4 upstairs shots for the first 30 - 60 seconds.
You earlier stated, or implied, that he was shot in his sleep, as was June you say. Were they awake or not? If they were awake, then how come? I thought you said the rifle was near-silent, and you also affect to imply that the rooms of these houses are virtually sound proof. What woke them? Be careful with your reply, because remember you're also asking us to believe Sheila slept through it all.
If they were awake and not asleep, then why did they stay in bed? Or did Nevill get up? if Nevill got up, what was he doing? Press-ups? Flippancy aside, the question matters because you are asking us to believe Nevill only took four shots downstairs, despite the blood and pathological evidence implying otherwise.
I'm not convinced Nevill was shot upstairs at all, but I must acknowledge that the cartridge cases were found there and while the position of the cases cannot be relied on, if we say that Nevill took his shots on the stairs and downstairs, then we have to explain why and how up to four cases have made their way upstairs.
Part of the explanation will be that the projectile cases have ended up on the landing from shots fired on the stairs, more likely with Sheila facing in the direction of upstairs, but possibly with her firing down the stairs towards Nevill - because the cases could have ricocheted off the walls and back on to the landing.
It's still a problem for the defence, though - I must admit that.