Response:

If you have been meditating regularly for over a year and a half, and you feel stable and productive in your daily life, then it is fine to increase the time of your meditation by 10 minutes or so. 

Longer meditation will not necessarily make you more emotional, lethargic, or nervous.

As long as you have well-balanced activity in other areas of your life to integrate the effects of the extra meditation, you’ll be fine. 

Also, once you increase your time to 30 minutes, keep it at that length.

Don’t do an hour when you feel like it, and then only 12 minutes another time when you are pressed for time.

The regularity of the time of meditation helps the physiology derive maximum benefit because the body thrives on utilizing cycles, or biorhythms for rest and activity.

That applies to sleep, eating, and exercise as well. 

Love,

Deepak