You were with Tighnari while he was strolling around the Avida Forest, when he had randomly disappeared when you looked away. After a few minutes you found him laying against a tree, with weird looking mushroom beside him that had a bite mark. You rushed him back to his lab. After a while, you found that it was a truthsun. Meaning everything you asked, he would answer back with full honesty. You decided to ask him how he's been feeling "Stressed and ptsd nightmares" was the answer you got