Jan Vertonghen throws up on the pitch during Belgium vs USA
The United States held Belgium to a scoreless draw in large part because of some outstanding play from goal keeper Tim Howard. The game had to go into extra time, and the physical limits of players were being pushed.
Factor in the endurance of playing over 90 minutes in World Cup and the Brazilian heat and humidity and the conditions are too much. Belgian defender Jan Vertonghen obviously had some trouble dealing with it and vomited during the game, on the field presumably.
Not particularly gross imo but still a gif of a guy vomiting, so... spoiler cut:
[ Spoiler (click to open)]

Sources 1 & 2
I wasn't imagining things, then. Pretty sure he didn't say anything to anyone and was still clearly trying to recover when Belgium players formed a circle immediately before the game resumed.
edit: fyi, there's no 'nt: belgium' tag, lol
Raphael Varane reportedly spends night in hospital after suffering dehydration
The Real Madrid defender appears to have suffered the heat more than most in Brasilia during the 2-0 victory for Les Bleus. According to Spanish site Sport, Varane spent the night in a Brasilia hospital as a precaution due to acute dehydration. It has been reported that players lose at least two litres of water during a game in the intense Brazilian heat. He is still expected to be fit and ready for the quarter-final against Germany on Friday.
Source
I cannot imagine how Qatar 2022 is going to be like...