Primary tests:

CBC
Chem panel
Urinalysis
Toxicology Screen
Titers for tick-borne diseases such as Lyme or ehrlichiosis
EKG

Secondary tests:

TSH - if EKG is not normal
Echocardiogram - to rule out DCM
Chest xray - to rule out lung pathology
Bile Acid test - to rule out PSS

Tertiary tests:

CAT scan
MRI
Mylogram
Spinal tap with fluid and cell analysis

If possible, a veterinary neurologist should examine the dog or a thorough neurological examination be preformed.