mood swing,mess up,silently hurt?

salam..
..actually I do love having a busy life rather than having lot of free time and doing nothing.supposedly right?

but..all of sudden my mood swing very badly(unbalanced hormone probably??)
then,,i became some kind of weird! feel lazy to study..even so lazy to smile at anybody..and one day after class,while waiting for the bus going back to akass,,there was a junior asked me wether there is anyone sat next to me..then without any smile on my face and with tensed expression..
i said ''xder,duduklah''
then,I realized something.. eh..cik matuz..cannot behave like that,,we are muslim then we are brother and sister..so how come you be so not-friendly?

so what to do? be optimistic and keep smiling!i alway remembered a phrase from a sister
''in any circumstances even hard to smile,please be nice to others,we have to..!''
May Allah bless us!
wallahualam..