Did my dog just have a heart attack?

I was watching TV with Peanut, my 10-year-old shepherd mix, laying on the floor at my feet.  She jumped up suddenly and seemed agitated, turning a couple circles like she was going to throw up.  She sat down as I reached for her to comfort her and kind of hunched over.  Which is a normal puking position. 

She stood up abruptly, her legs buckled and straightened one at a time, making her totter and struggle to get her footing.  Then she collapsed to the floor. 

I wanted to freak out but tried to stay calm.  I laid down on the floor, shooed Angel away, and held Peanut until her breathing slowed down.  I looked into her eyes trying to decide if her pupils should be that large.  Were the pupils blown?  Had she suffered a brain trauma?  Then she sighed and  laid her head on my arm.  I laid on the floor for about 20 minutes just petting her. 

Angel lay near us on the floor, but not touching either of us. Which is very unusual.  Angel likes to be in contact with the members of her pack.

I was quite relieved then Peanut moved first one front leg, then the other to lay across my arm next to her nose.  I was terrified to find out if she could stand on her own or not. 

After a bit, the floor got too hard.  I stood and picked her up, giving her no opportunity to stand.  I put her on the couch. positioned her across my lap, and petted her more.  

Angel came up gently onto the couch and laid next to her, not bumping, pushing, or laying on Peanut.

After about 20 minutes, it was time to go upstairs to bed.  I was quite relieved when Peanut jumped down off the couch on her own and was steady on her legs.

Still, I am concerned.  She has an enlarged heart and arrhythmia.  Did she have a heart attack?  A stroke?  Is this a harbinger  of the end of my beloved princess? 

We already had a cardiology appointment scheduled for today.  I hope he has some answers.