Not a big fan of BCAA on its own - that are not from whole protein sources, but the BCAA dosage studied are 60g - that's 5-10 times what most supplements suggest taking standalone/without other food.
BCAA competes with tryptophan so yes it will lower serotonin levels - therefore interfere with mood and sleep. That's why worst thing to do is to take BCAA at night unless you're severely catabolic, though a whole protein still better for many reasons. If you have pre-existing anxiety or low/ fluctuating mood issues, then stay far away from standalone BCAA as serotonin helps regulate impulsive/ high risk taking and anxiety driven behaviours. I've seen guys get jacked on BCAA taken pre-workout, which helps their workout, but not their temperament.