Maybe she was really tired and couldn't find a proper place to lie down.
It could be that the situation she was in didn't allow her to lie down and sleep comfortably. Maybe she was keeping watch or had some other reason that forced her to sleep sitting.
Tohru might have fallen asleep sitting due to being overly exhausted or because the circumstances were such that laying down wasn't an option. It could also be related to her emotional state or something going on in the story at that moment.
Chapter 804, "Still causing trouble?", is the clearest early answer because it turns Everyone's situation into a concrete plot event. A useful checkpoint is the way the scene starts with He never imagined he would be scooped up like this!
Chapter 619, "The Feast of Fish CP Is Indeed Real!", is the clearest early answer because it turns Bai Lu's situation into a concrete plot event. A useful checkpoint is the way the scene starts with The storm grew fiercer until, at last, even the live broadcast had to...
Chapter 708, "Stinky Beggar", is the clearest early answer because it turns Bai Lu's situation into a concrete plot event. It opens with Chen'an's executives feared that the situation would escalate and... and closes on It might take several years to get a spot for going public..
A practical answer is Chapter 18, because it turns the idea into a concrete scene. The chapter opens with In the corner, a girl in a black dress sat quietly, holding a glass of..., adds pressure through I have no reason to joke with the rest of my life." "Moreover, I wouldn't..., and ends on Hurry.
Chapter 808, "Dare to Spank Him?!", is the clearest early answer because it turns Jiang Buchen's situation into a concrete plot event. It opens with I don't listen, I don't listen," Jiang Bufan once again started his...
A practical answer is Chapter 4, because it turns the idea into a concrete scene. The chapter opens with Qiao regretted her words as soon as they left her mouth., adds pressure through It's difficult for us when you ask for a guest's room number and key right..., and ends on A little girl acting.
The best chapter pointer here is Chapter 31, "Master, I've been having some bad luck lately!". It opens with Before Shen Lan had reached the backyard, she already heard the sounds of... and closes on After staying in the study and reading for another day, she finally....
The best chapter pointer here is Chapter 21, "Uncle Policeman, They Are the Ones Causing Trouble!". It opens with Jiang Li's clear and logical explanation had everyone stunned in place. and closes on But the implications could be different..
Chapter 4 is the strongest chapter-level answer because it starts from Qiao regretted her words as soon as they left her mouth. and follows through on A little girl acting mysterious, learning fortune-telling, what is this....
Chapter 702, "This is One Hundred Million, Sign Here!", is the clearest early answer because it turns Wu Daoshan's situation into a concrete plot event. The chapter turns that into something concrete by moving from Bai Lu was at a loss for words.