About 12 months ago Peliroja allowed me to have a go on her fixie around the carpark at the pub on last years Pie Run.
It felt very strange but induced a grin bigger than Cheddar Gorge.
I spent the next few weeks contemplating the purchase of a fixie but hesitated due to having all the same concerns as you have now.
Eventually Marj pursuaded to me buy a Langster whilst we were in a shop in Helston on holiday last year.
I changed the rear sprocket to a 17t to give me 65"( I think) to cope with the "fully-formed" hills hereabouts where I live.
I now prefer to ride the fixed other than my geared Trek.
It gives great grins,a sense of satisfaction & goes uphills with much less effort than you expect.That flywheel effect is a strangely pleasant experience.
Don't fret about spinning downhills.If it gets too much just use the brakes.
So I suggest:-
if possible, borrow one to try before you buy
doing that,if you don't die
jay eff dee I
In my case Peli has a lot to answere for
Thanks Peli