Hello I am Dr. Joey. Thanks for trusting me to help you and your pet today. I am a licensed veterinarian with over 15 years of experience. I look forward to working with you.
There are certainly several possible causes for his fit yesterday and then inability to rise today. The first concern is that he injured his back (slipped disk). If the case, then the sooner he sees his veterinarian for treatment, the better.
My second concern is this may not be orthopedic or neurological but there is something larger going on (the drooling as a clue) such as a tumor that is bleeding and causing weakness from anemia (splenic/liver tumors are common causes in this breed). You should check his gum color and if it looks paler than normal or white, then this is an emergency, and please get him in right away. Some dogs have episodic bleeding and therefore, no obvious color changes but they are weak.
I wish there was something easy I could recommend do at home, but the fact he cannot rise and this has not improved, even though he is in good spirits, indicates he really must be examined today. Hopefully, you have some help to relocate him to the car. If not, then perhaps see if there is a mobile veterinarian in your area that can look at him today.
Please keep me posted. I am always happy to answer followup questions. You can reply to this question at any time to submit a followup. My goal is to provide you with excellent service today. If there’s anything else I can do, let me know – it’s been a pleasure working with you and I hope to assist you again soon! Kindly submit a rating as you exit our chat.