Mild symptoms such as difficulty calculating distances or split times are not truly confusion. Inability to follow a trail or remember orientation details (name, date, place, events) should be taken seriously. Confusion should typically be regarded as a red flag regardless of the cause. There are a few causes such as sleep deprivation that may be less concerning.

Consider the environment

Heat
Heat related illness can cause confusion, especially more significant heat illness such as heat stroke. If conditions are hot and you or your runner is confused immediately begin cooling and seek medical attention. The quicker you can cool the less dangerous this is. Immersion in a creek is best, other methods such as spraying with water and fanning, ice packs, and getting out of direct sunlight are also helpful. 

Cold
Hypothermia can cause confusion. If you are racing in the cold and feel cold and confused you need to warm up. If you are still shivering, this is a good thing and suggests the early stages of hypothermia. In this case, put on more dry, warm layers and increase caloric intake (warm fluids are great). If you are no longer shivering you will need someone to warm you.  Warm blankets, indoor heating.

Altitude
High altitude is typically considered to begin at 8,000 feet although you may feel some effects at lower elevations.  Most of the dangerous complications of altitude occur at over 10-12,000 feet. If you are racing at altitude, regardless of acclimatization you are at risk. You are at increased risk without acclimatization. Confusion at altitude is concerning, especially with other symptoms such as headache or poor coordination. Descend immediately and seek medical attention. You may be at risk for severe complications of altitude such as High Altitude Cerebral Edema. Dexamethasone (a prescription steroid) is part of treatment. Of note it is on the WADA banned list so should not be taken as preventative treatment in a sanctioned race.

Consider fueling and hydration

Hydration
Dehydration does not typically cause confusion except in extreme cases but overhydration and hyponatremia (low sodium) can. Have you been “drinking to thirst” or drinking substantially more than this? If you have been drinking too much and are confused you may be overhydrated.  NOTE: you can be over hydrated even if you are using electrolyte drink and not just plain water. Look for other signs such as nausea, swelling in the hands or legs or weight gain (these are not always present).  If you have been drinking too much and are confused, you should stop and seek medical attention. While stopped don’t drink more water but you can drink a concentrated sodium solution such as 4 bullion cubes in 125mL water (you may want to flavor this as well).

Fueling
Low fuel, i.e. blood sugar can cause mental slowness and confusion. Eat something with quick sugar such as a gel. If improved you can usually continue but keep a focus on fueling.

Recent falls

If you fell and hit you head and are now confused you should stop and seek medical attention.

Sleep

Sleep deprivation can cause significant confusion similar to being intoxicated in some studies. Usually this occurs in events lasting several days but can be seen to milder degrees in races that last 24-48 hours. Consider a nap if you are significantly confused.