18 month old male cockerpoo is a nervous dog, but this isn't nerves - he just sort of looks very scared and starts shaking - sometimes he'll get up in the night 2am or something like that, we'll get up to see if he's ok and he's out of his bed sitting somewhere shaking. There is no obvious reason, its like he's having some sort of attack. He calms down after about 5 minutes and then is back to normal. He's very thin but always has been so we assume its natural, never been a good eater, otherwise he is friendly and full of beans. Any ideas welcome.