Lassitude :Noun

a condition characterized by lack of interest, energy, or spirit

https://www.merriam-webster.com/dictionary/lassitude

I encountered this word in ch 19 of quicksand.”Helga met Dr. Anderson at the social affairs to which often they were both asked. Sometimes she danced with him, always in perfect silence. She couldn’t, she ab-solutely couldn’t, speak a word to him when they were thus alone together, for at such times lassitude encompassed her; ”

I have never seen this word before I actually thought it meant something along the lines of guilty accompanied by joy.I thought this because of what happened between them,but despite that she’s still around him.Now that I know that this word is basically saying she’s in a drugged like state I’m wondering if maybe it’s trying to become an excuse for her lack of action.