I would also recommend to call ahead of time to warn them.
Back in February, the morning of my flight to Sydney, my left knee got completely stuck and very painful, I could barely put the left foot on the ground without instant joint pain.
I still managed to get to the airport and asked if I could get at least an electrical car ride to the end of the hall (15mn walk) but they told at Changi me I had to "book and pay ahead" for this service.
I managed to crawl/jump/use the luggage cart to make it on time for my flight just to see another electric cart bringing someone else in exactly the same condition I was in. When I asked how they managed to get on a car like that, they just said that the Changi employees saw him in pain and offered a free ride.
Go figure...
Luckily the SQ team was very helpful and gave me about 15 pillows so I could lock my left knee for the whole 7-hour flight and managed to reach destination.
Julien