Quite an unlucky day

Good day everybody!
I own a 2009 Pontiac G3 wave which has been troubles free until today. It currently have 33700kms. First I was on the highway and I saw the speedo moving up and down. I was going around 3200-3300rpm in fifth gear so basicly 118-120km/h but speedo was showing sometime 0 some time 60 then back to 120 down to 80km/h and did that for over 2 hours what could be the cause? Then there was a taxi in front of me who lost it's top light which I've been hitting hard. I then pull over on the sholder to look for damage everything seem to be fine no leakage etc. I then heard a strange uneven noise like an unsteady idle I went inside the car to look at the RPM and it was steady around 800rpm which is perfectly normal. I drove back home and on my way I saw the temperature gauge went down completely. During my drive back home I felt that the clutch was not reacting normally but a similar way that I expect when I just start driving at -15C. I wonder if it's been acting this way because the engine was cold? Finally when I made it to home I went outside look and feel the engine temperature it's seem to be cold and the fan was working continuously. I let the engine run at idle for a couple of minutes and I saw the engine temperature rising. What could be the cause of all of this? Thanks!