A quick look at the meaning of Frühjahrsmüdigkeit - an ailment that many Germans suffer from in spring time, but that is rest of humanity has never heard of :)
das Frühjahr, der Frühling, müde, die Müdigkeit
This root is not 100% certain and it is only mentioned in German sources, but not in English ones.
The core idea of the root (if it existed) was something along the lines of:
being string willed, striving towards
It is thought to be the origin of the Latin mōs, which was a strong custom or will, and which is the origin of moral.
The other likely English relative is mood.