Google Translate can be good for translating single items of vocabulary or for translating short sentences from foreign language into ours, to get a grasp of what they mean. However, translating big sentences from your native language into the language you don't know and then tattooing the result on yourself would be pretty foolish. There aren't any perfect online translators and having a tattoo with an error in it would be rather embarassing.
I took the sentence you wanted and then used Google Translate to translate it into Polish, my native language. What I got was:
"Strzeżcie się, żeby jego cień nie może obciążać sen z okropnych koszmarów".
which is, well, not correct. The closest it could be is "Strzeżcie się, żeby jego cień nie mógł obciążyć waszego snu okropnymi koszmarami". And there could be some better translations, really (I don't feel like "obciążyć" is the best possible verb to use here, but I can't really think of anything better right now). So, as you can see, using Google Translate to translate a complex sentence will most likely end badly.
So, in short, I hope you haven't done that