I go right after work as well. It's the first 10 minutes that are hard for me. Around 5 p.m.-ish I start to feel sluggish and I'll always start off with stretching followed by a warmup that will wake up my entire CNS. I'm usually good to go afterwards. But I do believe in the mind over body thing. If your mind has any doubts at all, you're more likely to fail or have a bad workout.