It's trouble all right. You need a fermentation bucket or at least a 23 litre carboy with a blowoff tube.
You shouldn't try to ferment it in your 5g carboy. But if you truly have no other option, ferment as cool as whatever strain you are using will allow (my guess is that you don't have a temp controlled ferm chamber), even if you have to rig up a swamp cooler.
2012 Canadian Brewer of the Year
2013 Canadian Brewer of the Year