Have you talked to your vet or taken Nala in for an exam? Two thoughts come to mine. First, canine alzheimer's. There are some drugs available that help with this. Most likely your vet will require a blood panel first to make sure kidney and liver are functioning at normal levels before prescribing medications.
Second thought, maybe Nala is developing some separation disorder. You might need to speak to an animal behaviorist if this is the problem.