Run Interval Training
This is a 20 minute session that looks very easy to do. After all, what's 20 minutes? Best part is. Consistent interval training of just 20 minutes a few times a week is probably more effective in increasing stamina & performance than hours of running at the same pace.
Well, it looks easy but I was breathless and seconds seemed like minutes when I did it today.

3 mins - easy jog warm up
3 mins - medium/fast running
60sec - walk or stretching
90 sec - fast run
60 sec - walk
90 sec - fast run
60 sec - walk
90 sec - fast run
60 sec - walk
90 sec - fast run
60 sec - walk
90 sec - fast run
60 sec - easy jog

Give it a try. Then you'll know what I mean by seconds feeling like minutes!