Sentence:  The problem here was the translation of "period" by German "Periode". In describing the symptoms we may say that in connection with "Schlaf" the German word "Phase" would have been a better <WSD>collocation</WSD>. 
Meaning of the word marked with <WSD> tags:  A sequence of words or terms that co-occur more often than would be expected by chance (i.e., the statistically significant placement of particular words in a language).