It's definitely worth considering selling and then either taking profit or buying back in if/when it drops again. As someone already mentioned, it will depend on market conditions, but I would always at least check out the option. Most coins that rise that much overnight now will drop back within a day or two, so even if they don't drop back all the way, you can normally increase your holding. I did it a few times towards the end of last year, and although I could have made more by holding, I regret it less than not selling and watching profits evaporate.