Studies have shown^1-2 that simply smiling (even if you don’t feel like it) may lower your heart rate and reduce stress levels—regardless if the smile is genuine. One study suggested that by smiling, you may be able to reduce the intensity of your body’s response to stressors.¹ Looks like ‘turn that frown upside down’ may be more than just a cheesy saying.

Sources:

[1] https://www.forbes.com/sites/rogerdooley/2013/02/26/fake-smile/#2318f02a3676

[2] https://www.psychologicalscience.org/news/releases/smiling-facilitates-stress-recovery.html