Exact same thing happened to me. Everything you described I was like and also I knew what was in my head and I was trying to say it but it came out slurred and completely the wrong words. It was a migraine. The midwife I was working with at the time freaked out and thought it was some mini stroke or pre-eclampsia but an older midwife who came to get me recognised it as a migraine and made me some old caffeine trick she knew and fixed me right away.