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 Malinois, a change in drive is the thing to notice. A dog who suddenly startles at the door, bumps into things at dusk, loses interest in training or gets irritable may be losing their sight, have an underactive thyroid, or be in pain. It is easy to put it down to mood, and the sooner a vet sees it, the better. A seizure can look like shaking, paddling legs, drooling or a blank stare. Keep them away from stairs and the pool, do not put your hand near their mouth, time it and film it if you can, then contact your vet. 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 is most common in large, deep-chested dogs, so skip walks and hard play shortly before and after meals.
They'll still ask for an eleventh minute. If they stop asking, tell your vet.