My 2 year old dog died suddenly

My beautiful boy teddy bear died at home 4 days ago he was 2 years old healthy dog he was on the trampoline with my son my son came in and left him out there my daughter shouted me I ran out and teddy was confused slobbering and couldn’t stand on his back legs I carried him in the house and he seemed to settle an hour later he had some sort of fit he calmed back down but still was weak and couldn’t stand. Then he starting jerking and he died. My heart is breaking not knowing what caused this does anyone have any clue what could of caused this?