Westerman, 19, was hurt during the first half of the Tigers’ 68-22 defeat and went into spasms.
The game was held up for 12 minutes as he received treatment from medical and training staff, and Westerman was then taken to Wakefield’s Pinderfields Hospital for observation.
Head Coach Terry Matterson said: “Everything’s fine, his full memory is back and everything’s good, and that’s fantastic, that’s the most important thing today.
“It looks like he’s trying to get out of hospital.
“It was just a bit of bad luck to be honest, which is good, I’m glad there was no illegal play.”