Never been so productive in my life. 
You remember that scene from Oppenheimer where he cannot sleep because he sees all those fusion stuff? 
That's my every evening, but I'm designing solutions in my head, solving problems until I pass out into void. 

I've created more code last quarter then I did last 5 years combined. And that's just the beginning
My new contract is top match for my skillset and experience. 

This will be my opus magnum. 
I'm in my prime time. 
I've been working last 10 years to be here and I've deserved every minute of this.  

 I hope you are not coding weapons of mass destruction or something evil then... 

 I've decided years back that I will never be working with something involving military or gambling. 
I cannot write the details coz I'm treating seriously all NDA's but worry not. 

 I hope you are not coding weapons of mass destruction or something evil then... 

 what is your secret of such productivity? 

 Just doing the right stuff which utilizes 100% of your skillset and pushing you to expand it further. 
I'd recommend you to read this book. 
https://www.amazon.com/Drive-Surprising-Truth-About-Motivates/dp/1594484805?ref=d6k_applink_bb_dls&dplnkId=eb7392d1-48fe-4df7-9194-7a14400db874