Cathe's workouts gives me a 'good' tired feeling also, but I have great energy on even though my body is tired. Hope that made since.
OP, you may want to alternate harder workouts ( i.e. intensity, tabacize, Hiits etc ) with milder workouts (e..i. step, premixes or body parts workouts) and definitely eat well, and get plenty of sleep.
When I am well rested, well hydrated and well fed - I am a beast at 48. I love it when I make every step, squat jump and power 15s. But if Im not taking care of myself, I am a slug.
HTH