my dog's very weak

My dog is very weak (can barely stand up), drooling, and has difficulty breathing. She was so active earlier today but she suddenly went a bit sluggish (like when a person is drunk) and had convulsions a little bit (I really thought that she was dying). Then, the convulsions stopped, she's already able to sit up (not yet standing on her 4 paws) but still seems to be out of breath, drooling, and a bit weak. What is happening to my dog?

Hello!  I can tell that you're worried and I'm afraid that from here I don't know what is happening to your dog - possibilities are as diverse as a fit, Addisonian collapse, respiratory disease, hypoglycaemia - but I hope that you are at or on the way to the vets in order that they can find out. It sounds as though there has been weakness and difficulty breathing, then possible convulsions, none of which are things you can treat at home (certainly not in the UK - where are you?) Does your vet have an emergency service?  They would be the best people for this one.  Always phone (either first, or on your way). Best of luck.

Rereading this, from what information I have, a fit would be on my differentials (possibilities) list.  Dogs go from normal to a bit 'odd' or 'spaced.'. The fitting phase doesn't last for long and they wake a little disorientated.   But there are so many possibilities and this is definitely one for your vet.