It is not possible at this point in time to give a clear diagnosis on his condition. As soon as further information becomes available, it will be communicated via www.IrishRugby.ie and media outlets.
Unfortunately due to these symptoms, Simon will be unable to take any further part in the World Cup and will be returning home when he is given medical clearance to do so.
Ireland coach Eddie O'Sullivan said: "The thoughts of the management and all the players are with Simon at this time. He is an incredibly popular player and is a key member of the squad and it was a shock to everybody when we heard the news."
The Irish Management have decided to call in Munster prop Tony Buckley as a replacement for Simon and he will depart from Ireland as soon as possible to join up with the rest of the squad.
With Simon being unavailable, it means that Bryan Young will move up into the replacements as prop cover for Sunday's game against Argentina. The two positions left open for the starting and replacement hooker berths will be resolved once both Jerry Flannery and Rory Best, Simon's younger brother, complete fitness tests this afternoon.