Might be worth having a chat with the vet to be safe.  He's older now too, and maybe a bit less tolerant of the dog - like a grumpy old man - and he maybe gets a bit more tired than he used to, many elderly people like to have a cat nap during the day.  But as you're concerned, I would have a word with the vet.  Bailey's conditioning cubes sent my warmblood nuts and really hyper, so I'm not too sure about Bailey's feeds to be honest, but I don't think it will be the feed to blame in the long run.