If ur really tired then its may be dangerous to lift heavy. If ur tired enought for it to hav an effect then have a rest day, or have a nap before u train. If u do bag work u'll have bad form and may jar wrists as ur not punching properly. Best thing would be to swim, as even if u have bad form, its not gonna hurt u. that or get on the Ginsing!!!!!!!!!!!!!!!!!
"Turn your face to the sun, and your shadows will fall behind you."
"While your looking to hit for points, we are breaking legs and taking you by the neck"