if i leave my external hd unpluged for extended periods of time will i lose my data? i know when i leave some portable devices off for a while i lose the data im not sure if they store data the same way. i just want to make sure.

No it will be fine, basically an external HDD is the same as the one in your computer just exposed with a shell on it, so it wont be a problem. Just as always be carefull when you transport it as they can damage very easily with small knocks, of which will then stop you from accessing your data