Feeling sad after a good day

I have a love-hate relationship with sunny days because in the past I have felt pressurised by myself (no-one else) to make the utmost use out of them, which inversely causes me to cower away from doing anything and then feeling disappointed in myself. I have the learned association with sunny days that they are good per se because everyone including my dad, who probably helped form the opinion, thinks they are. Problem is it spins my mood the other way occasionally, and if I end up accepting doing nothing as a means of relaxing and avoiding the known habit of stressing about what to do on the sunny day, I likely just won't relax because I've let myself down by doing nothing. The example being that good and bad associations can live side by side. 

Your daughter's sadness could be a similar thing - she could feel pressurised to make the most of the intensely happy day, on the basis that they are valuable and don't come around very often. She might be sad due to acknowledging that it is at an end when she has come home from school. On the other hand, it could just be that she says she is content 'happy' when she is just placid inside, because the actual happy emotion is like a sensory overload, too much emotion to process. Another possibility at play is that she tolerates school and knows how to cope, but the sadness is that when she has a really good day on top of the coping, she knows that coming home will involve ending her one-off day of thoroughly enjoying school. She could be pretty acutely aware of her emotions, just have no idea of explaining why they are there. It does make sense to want to figure them out as it might help you find the thread of how to make things easier for her by perhaps connecting. 

It's good that she has cheered up. It's hard not knowing why as I suppose you want to 'bottle' the why as a magic potion!  

Just thought I'd lend my thoughts. Take a pinch of salt though and use your judgement on what I've put. I hate sticking my head above the parapet!

I have a love-hate relationship with sunny days because in the past I have felt pressurised by myself (no-one else) to make the utmost use out of them, which inversely causes me to cower away from doing anything and then feeling disappointed in myself. I have the learned association with sunny days that they are good per se because everyone including my dad, who probably helped form the opinion, thinks they are. Problem is it spins my mood the other way occasionally, and if I end up accepting doing nothing as a means of relaxing and avoiding the known habit of stressing about what to do on the sunny day, I likely just won't relax because I've let myself down by doing nothing. The example being that good and bad associations can live side by side. 

Your daughter's sadness could be a similar thing - she could feel pressurised to make the most of the intensely happy day, on the basis that they are valuable and don't come around very often. She might be sad due to acknowledging that it is at an end when she has come home from school. On the other hand, it could just be that she says she is content 'happy' when she is just placid inside, because the actual happy emotion is like a sensory overload, too much emotion to process. Another possibility at play is that she tolerates school and knows how to cope, but the sadness is that when she has a really good day on top of the coping, she knows that coming home will involve ending her one-off day of thoroughly enjoying school. She could be pretty acutely aware of her emotions, just have no idea of explaining why they are there. It does make sense to want to figure them out as it might help you find the thread of how to make things easier for her by perhaps connecting. 

It's good that she has cheered up. It's hard not knowing why as I suppose you want to 'bottle' the why as a magic potion!  

Just thought I'd lend my thoughts. Take a pinch of salt though and use your judgement on what I've put. I hate sticking my head above the parapet!