The 19-year-old loose-forward was taken off on the half-hour mark of the game following an innocuous challenge by Saints’ Lee Gilmour.
Westerman spent a 12 minute period on the ground, where he endured a series of fits but will now miss the Tigers’ game against Celtic Crusaders in Bridgend.
Despite making a full recovery, Tigers’ spokesman, David Smart, said that Westerman was still struggling to remember the incident.
“We’re going to be careful with him,” said Smart. “Joe came in again this morning but Terry sent him home to rest.
“He says he is feeling okay but he doesn’t remember much of the incident. He is going to have a further examination and Terry will assess him next week.”