What to do if you're very lazy or lethargic and just don't feel energetic enough to pursue many tasks? 

Here's a desi Nuskha that was featured in the 1st December 2011 episode of Astro Uncle on Tez Channel:

You can follow it if you believe in Pawan Sinha ji. 

Laziness: Take ½ tsp of coriander seeds, soak them in the water overnight and drink after 10 minutes  of waking up. You may strain the seeds and then drink the water. 

Eat some bhuna hua chana- bengal grams (20-25 tsp a day) especially in winters, they should be fried in cow ghee and some black pepper should be added as well. These chanas give a lot of energy to the brain as well as body.