Convulsions

Our shitzhu one night, started to convulse out of nowhere. My mother calmed her down and just petted her. A couple minutes later, started to convulse again. My mother asked me what causes these convulsions. Any ideas?

[Aleda M Cheng, D.V.M., C.V.A]

Convulsions are seizures.  Seizures can be brought on by toxin ingestion, infections and head trauma or abnormalities in brain function and more.  Your dog really requires a complete work up by a vet to determine the definitive cause of the problem.  If every thing turns out to be normal in your dog than the cause is idiopathic seizure disorder which just means seizures of unknown cause.  Seizures are highly treatable with the proper medications.