Yes
Yes
Yes
Yes
Lethargy is basically a state of being tired or lazy. It is a very vague symptom, and though can occur in narcotic abuse, is not specific enough by itself to be of much value.
No--lethargy is a symptom of a health problem. See a vet ASAP.
Hypernatremia is especially dangerous for children and the elderly
Severe hypernatremia has a mortality rate of 40-60%
Hypernatremia can cause neurological damage due to shrinkage of brain cells
High serum sodium levels (hypernatremia ) occur at sodium concentrations over 145 mM
--> causes of hypernatremia --> increased serum osmolality --> water shifts from cell to plasma --> cells shrink ---> manifestation
Severe hypernatremia, with serum sodium above 152 mM, can result in seizures and death