That greatly depends. I've been electrocuted twice. No serious injury, just some numbness and a shocking feel. It was a damaged lamp and stupid me stuffing things into an electric socket. Learnt how electricity works,the hard way, now I respect it. When we talk about high voltage like train and power lines, those can electrocute you even if you just get close to them and can fry you in seconds. Afaik the most common cause of death is heart failure. How quickly you'd loose consciousness is actually an excellent question.