Just as when you are thirsty you don't concern yourself with the complex biochemical processes that led to that state. Nor do you try to analyze just what constitutes that state. You may, conceivably, just say to yourself "I'm thirsty." Usually though, you simply go and get a drink, and think no more of it.
When I was younger, I got thirsty but didn't realise it. I got mild dehydration sometimes because of this. When I was a student, I once gave up coffee for a week, just to see if I could. I didn't crave coffee, but I had a constant bad headache, so decided the withdrawal symptoms weren't worth it. Only later did I realise the headaches were mainly dehydration: when I gave up the coffee I didn't think to substitute anything else.
Later on, I started making a connection between a certain physiological state---a particular feeling in my mouth, throat, and head---and the fact that if I didn't drink something soon, I would get a headache. I eventually deduced that this physiological state must be what people refer to as "thirst".
Now, when I recognise that state, I say to myself "ah, I must be thirsty", and go and get a drink. But I definitely do have to think about it. The experience is almost totally intellectual, and quite easy to ignore (despite the foreknowledge of the headache), qualitatively unlike hunger, where something inside me is going "food, food, food! now!!"
Okay---writing all this has made me recognise that I'm currently experiencing that physiological state again---I've analysed the state, and decided it means that I must be thirsty. So, having thought about it, I'd better go and drink a glass of water.