It's the middle of winter and there's no fire or other means to stay warm. Hypothermia would have set in within minutes after Ottway crawls out of the river. Ottway takes off his heavy jacket after getting out of the river, and in later scenes he's not wearing his hat or gloves either. One of the symptoms of severe hypothermia is a false sense of warmth, in which many sufferers take off various layers of clothing (called paradoxical undressing). Ottway even references feeling warm when the first survivor is dying. However, he is perfectly lucid and able-bodied when preparing to face the alpha wolf, so there would have to be some Artistic License – Biology going on.
