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 Bichon, watch their skin, their water and the way they move. Licking their paws for hours, or shaking their head, is usually itch or ear trouble. Straining to wee, blood in their wee, or drinking far more than usual needs looking at the same week. A skip in their step after a run can be their kneecap. In an older Bichon, 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.
They'll keep working for their dinner. If they stop doing the tricks, or limp afterwards, tell your vet.