I agree with 14+.
Did something startle him awake to make him attack? It almost seems like he had redirected aggression as 14+ stated, which normally occurs when a cat will see another cat outside and can't get out to fight so it attacks the closest thing, human or animal. One of our senior members has a cat with this and uses Feliway which I believe works for her.
First step is neutering to get rid of the hormones, and hopefully bloodwork will precede the operation. You many want to add a urinalysis to check glucose levels.
Cat maid to:
Puddles, female Himalayan (16 yrs)
Jasper, male Ragdoll ?? (approx 9 yrs)
Sweet Pea, female silver tabby DSH (approx 7 yrs)
Rose semi feral, a cpietra rescue, female tabby (approx 6 yrs)
Snowball RIP (1991-2005)
In a cat's eye, all things belong to cats.-English Proverb
“While we are free to choose our actions, we are not free to choose the consequences of our actions.” Stephen R. Covey