[That is part of the reason, and probably some of the drugs still in his system affecting his powers. Which is also why he didn't just immediately leave to go carry out his threat.]

The effectiveness of their drugs has worn down. I don't need to be at full strength to eliminate everyone in that building.

[Though he hasn't exactly gotten up to leave. He's really thinking about how he wants to. Cloud will probably get in the way, which will be a problem.]