It really depends on WHY i am happy/sad/relaxed tbh. Generally,
Lana
Happy: Her popier songs (Go Go Dancer, DICWB, OTTR, Lolita)
Sad: Ride
Relax: Money, Power, Glory & Shades Of Cool
Gaga
Happy: TEOG
Depressed: TEOG

that song has a double meaning to me
Sad: ARTPOP

Fooled Me Again
Relax: Summerboy
Florence
Happy: DDAO
Sad: Mother
Relax: SIO
Angry: Swimming
Taylor
Happy: Holy Ground, NR & SIO
Relax: Style
Vengeful: BS & Better Than Revenge
ShawnMendes: You Belong With Me & Love Story