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 Chinese Crested, watch their skin and the way they walk. If a spot spreads, a sore will not heal or a lump grows, contact your vet. A young Crested who limps or stops using a back leg can have a hip or kneecap problem. In an older Crested, drinking far more than usual can be their kidneys. 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 the heat, and that can cost weeks.
They'll keep choosing the sunny window. You keep choosing the shade, and if a patch of their skin changes, contact your vet.