How do I know?

The title says it all.

I went jogging today, after days of fattening program in my hometown. Thanks to my mother's excellent culinary skills. Indeed, I gained a few kilograms within three weeks. In my attempt to compensate for that, I went jogging just now. I ran six laps, and I thought that I was going to stop, but I carried on to complete a total of ten laps. After completing my last 100 meters sprint, I was so damn tired I could die. Then a question struck my mind, How do I know that I am tired enough to call myself tired. Intriguing, isn't it?

According to the common definition of 'tired', how tired is 'tired'? How about happiness, sadness, and depression?

The problem to answer this is that you can not measure any sensations that you feel, nor can you compare it with others'. For example, no one can understand or comprehend the sensation of tiredness that I felt when I completed my 10 laps, for the simple reason that no one can feel exactly the same sensations as others.

One may try to explain one's personal sensation by relating it to the feelings that people commonly get when going through a course of event. For example, "I'm so happy. It feels like I'm flying up high in the sky!". Yeah, something like that. But again, people may feel differently about flying up high in the sky. Thus, to a certain degree, this attempt is not very successful.

So what's the seemingly-humongous problem? My definition of tired, or happy, or sad, or depressed is really personal, and it is most probably different with others.

How do I know when to stop running?
---When you feel tired.
When do I feel tired?
---When you think that you can no longer go on.
When is that exactly? How do I know that I can no longer go on?
---Hmm... when your body tells you so.
How does my body tell me so?
---through the emergence of tired sensation.
How 'tired' is enough to tell me that I can no longer go on?
---when you feel that the tiredness is enough to make you feel that you can not go on.
Not going anywhere, aren't we?
---yes, in the first place, your question is not necessary. You stop when you feel like it.
When is that?
---Sigh.... I do not know.

I myself am confused on what to write. I hope you can see the problem here? Our sensations are personal, strictly personal. No one can understand it completely. Maybe I'm mistaken but I think it is called quale with the 'e' of bed. so... Quale.

Implication? Hmmm, since you can not tell how tired is enough to stop yourself, why not put your fullest effort such that your body will forcefully stop you, for example, by fainting. As to the question 'How enough is enough?', put your fullest effort in it until you are at the verge of insanity.

What am I doing? I have an exam to prepare for. I guess some people may be able to tell where I come from by reading that piece of information.