Some of this is not a training problem, and treating it like one wastes time your dog may not have. If they are distressed when you leave, if they growl or guard their food, their toys or you, if they are frightened on the lead, or if anything about them changes suddenly at any age, contact your vet the same day. A tip from a website, ours included, is not the answer. If it cannot wait, contact your nearest emergency vet now.
With a Miniature Poodle, the things that look like mood are often the body. Slowing down and putting on weight can be the thyroid. Flat days and a picky appetite can be Addison's disease (the adrenal glands not making enough hormone). Hesitating in the dark can be their eyes. A sudden fit of trembling or staring can be a seizure. A first seizure, one that lasts more than two minutes, or more than one in a day is an emergency: contact your vet now. So is bloat (GDV, a twisted stomach): a swollen, tight belly, retching with nothing coming up, sudden restlessness or drooling. It can happen in any dog, though it is most common in large, deep-chested breeds. In an older dog, drinking much more water, a pot belly and panting are worth mentioning too. Tell your vet about any of it.
They'll find every piece of their dinner. If they start leaving some behind, tell your vet.