Mental clock, Bio clock and the clock

The Sun does not seem to set in Germany during the summer days. In winter it is dark by 4pm and sort of bright by 9am in the morning. In sharp contrast to this, in summer it is dark at 'I dont know what time' and it is bright by 5:30am.
At 10:30pm it is still bright. Some Indians like me sleep only when it is dark. This is what my 'mental clock' says. My 'bio clock' is dragging my eye lids down to a close because it's time to sleep. It is really a bit difficult to adjust as I am not a sleeper during day - Day is when the sun shines.
One cannot roam about because the shops close at 8pm irrespective what Sun does. They stick by 'the clock'. Trains and buses stop plying because it is late night. What is night? Time when Sun does'nt shine and it is dark and time to sleep. Here it is night by 'the clock' but our mental clock says (because of the definition of night) it is not night yet.
Oops!! When shall i sleep?