Why does my dog jump every 20 seconds as if bitten?

Hello, my two-year old male neutered shih tzu got groomed 5 days ago and has been acting strange ever since. Groomer is trusted. My dog was strangely sleepy on the car ride home, then the next day I noticed him depressed, lethargic, and increasingly uncomfortable esp. at night, often just sitting up staring at me all through the night. For 3 days, he has been jumping every 20 seconds, as if startled or bitten. He has no fleas. He did get a preventative flea treatment at the vet, but not the dipping kind so I have ruled out allergy to dipping. Poor guy hasn't slept! Any ideas? My groomer could not figure it out. Thank you!