Simon a very good sativa makes me more alert and I use a ABX vapen and sativa extract while I'm working keeps me very focused but I'm not talking about getting blasted but just "nice" I tend to come up with good problem solving (I program CNC Lathes to turn plastics for the wafer makers in the silicon valley), my days go by much better as I feel this improves brain functioning oh and my rhythm is getting tighter and tighter.
So couch potato can happen with a potent indica strain so choose wisely, and change at your age is great, your mind must be staying young kiddo. I'm a veteran cannabis users, so I advise caution with new users to avoid too much but to go easy to avoid any paranoia that comes from a little more than you can handle so early in your exploration.