Yes it is worrying but given he’s already had the all clear, the club haven’t called him back for further assessment and he attended the game it looks like it’s fairly minor. It could have been nothing more than him feeling a bit unwell but some caution was taken given the previous incident...
The article says he was given the all clear and actually travelled to the game to support his team mates so doesn’t seem to be too serious. I’m sure we’d have been getting him back to Lancing for further tests if there were even any slight concerns with his long term health.