Why did my rabbit die suddenly?

Question
I wonder if you can help me as I am wondering where I went wrong.
I kept & bred rabbits for many years as a teenager & about 2 years ago got a handsome rex cross(?english butterfly) male for my daughter. He proved to be the most sweet-natured rabbit & loved to run free in our walled garden playing with our cats.
2 days ago for the first time in months i left him in his hutch for the day as the weather was foul. He was fine and eating in the morning. In the evening, when i returned it was dark when i gave him his evening meal but I don't remember seeing anything unusual. But the following morning he was listless and when i picked him up he was quite limp.I realised he wasn't well so i put him in his run with plenty of hay in the covered area for him to be warm & cosy. That evening i returned from work thinking if he were no better I'd arrange a vets appointment, but to our horror he was dead and clearly had been for some time.
we were devastated & don't understand what happened. He was blooming with health and had had nothing different to eat/drink. His eyes, teeth, nose, anus were all clear & no signs of bites/ other damage.

What i keep worrying over is that a) I should have cancelled work & gone to the vet, but i just didn't know hosw sick he was, and b) that a laburnum tree we cut down a week before may have poisoned him as i saw him eat some leaves before i cleared it all away. Is this possible & is it poss that this would take a wk to affect him?

Any ideas would help as I'm feeling really bad .

thanks.

Answer
I am not sure if laburnum is poisonous to rabbits or not, but generally poisonous plants act pretty quickly on animals as small as a rabbit. A rabbit's metabolism is also very quick, which would further make it unlikely that it would not affect him until a week later.

The most common cause of sudden death with no real symptoms in rabbits is gastrointestinal stasis. This is where the hindgut literally stops moving. It can cause a very quick decline and death of a rabbit. Was he eating and drinking okay? Were his feces normal? Not eating or drinking as normal, or abnormal (or lack of) feces are two common signs of gastrointestinal stasis. Of course, since he was in an outside hutch, I am assuming the feces fell right to the ground. This could make it difficult to determine if his feces were normal or not.

Obviously you did not know how sick he was. However, for future reference, prey species of animals (like rabbits) are very good at hiding any signs of illness or weakness. So if they are showing obvious signs of illness, it usually means they are pretty sick, and they need to see a vet right away. I know this will not make you feel any better, but it can help prevent something like this for the future. I am very sorry to hear about your loss. These little guys sure have a way of getting into our hearts, don't they?