> Do you folks have a source of extra income which does not have anything to do with programming?

Why handicap yourself by ignoring one of your most useful and rare skills?

Use your programming skill to build a side business. Build some kind of service or API or something useful to others that they'll pay money for.

> I'm worried that getting freelance programming work will make me stressed and sick of writing code.

There's nothing wrong with sometimes freelancing - just don't be the idiot that tries to compete by having the lowest price. Double or triple what you think your rates should be. You'll avoid garbage clients and be happy about any work you get no matter how much of a clueless jerk some client is.