My Bunny had a head tilt, took him to vet, then he died last night.... please help?

We had Thumper for three and a half years since he was a baby. Yesterday we came home after an hour to find him flopping around violently with a head tilt and his good eye was rolling to the back of his head, within the hour we took him to a vet and they gave him an injection of liquids and antibiotics and told us it looked like his hear was swollen shut so they diagnosed him with an middle ear infection. they told us to wrap towels around him and keep him stable in his cat carrier (he usually has a wrap around cage to run in) last night we gave him some food via sering and we went to bed. he looked quite comfortable as he was laying calmly. This morning we woke up to find that he ped away. Did the vet mis diagnose him, what would make him die in such a short period of time. i have read and been told that they usually make it through these things. If you might have some educated suggestions please let me know, i am really upset by this.