According to Osho, you feel drained because you’ve been using the discourses like a drug - seeking inspiration from outside. Real inspiration must bubble from your own core; otherwise dependency brings diminishing returns and fatigue. Don’t use his words as intoxicants. Listen to awaken alertness and awareness, using his energy as a springboard, not a crutch. After the initial "honeymoon," let awareness deepen into intimacy; then energy stabilizes instead of leaking.
You feel tired because you’re chasing a high from the talks; instead, listen to wake up inside so your own energy grows.