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 Cavalier, watch their breathing and their neck. Faster breathing while they sleep, a cough, tiring early on walks or fainting can all be the heart. Scratching at the neck or ear, yelping when the head is touched, or not wanting a collar on can be Syringomyelia (fluid-filled pockets in the spinal cord). In an older Cavalier, pacing or staring at night can be the start of Cognitive Dysfunction Syndrome (dementia in older pets). Bloat (GDV, a twisted stomach) can happen in any dog, though it is most common in large, deep-chested breeds. A swollen, tight belly, retching with nothing coming up, sudden restlessness or drooling is an emergency: contact your vet now. It is easy to put the rest down to habit or age, and that can cost months.
They'll keep your lap. If their breathing changes while they sleep on it, call your vet.