Using a first aid analogy, there are signs and symptoms. Symptoms are what you're ferling and experiencing, and signs are changes that can be percieved externally, so if your symptoms of thirst and hunger are similar, you can also look at signs; is my tongue unusually dry, have I recently had a drink, has my sweat changed? That sort of thing.

Ideally you want to be assessing your symptoms, whilst ignoring your brains "default" response to them. Does anything hurt? Do I feel fully alert? Do I feel weaker than usual? Notice the actual sensations from your body, and you can work out what different patterns of them mean.