My name is***** and I will try to answer your question this morning.
Head/neck stretching can be nothing, but it can also be suggestive of some health problems-
-behavioral, just to get more comfortable
-mild neck pain (muscle stiffness, disk disease, inflammation in spinal column)
-discomfort in abdomen (pancreatitis, foreign body in stomach, liver disease)
I would recommend taking your pup to your vet for a thorough exam, including an orthopedic exam to check for neck and back pain as well and blood work, including triglycerides (very commonly elevated in schnauzers and can lead to pancreatitis), the pancreatitis test, urinalysis and thyroid level.
Does this help? Do you have any other questions?