Our 11-month old collie x has recently begun having what I can only describe as nightmares. He yelps and whimpers loudly in his sleep. It's quite distressing to hear. We don't wake him up when he's doing it in case it upsets him further, plus we don't want to reinforce that there's something to worry about by giving comfort . He's a rescue dog - we have had him since he was 5 months old and know nothing about his history, we don't think he was abused but don't know for sure. He doesn't appear to have any fears when he's awake and is usuallly a very happy chappie. He recently had a ripped claw removed at the vets and was a little traumatised by the experience, but the nightmares pre-date this anyway. Any thoughts?