Swimming is nice and I do it once a week, but it's cardio.

More intense exercise produces endorphins, just as heroin does, and with little time and effort compared to cardio. You will feel really, really good. But, you have to do lifting exercises with something so heavy you can only lift it 5 to 8 times before crapping out. Ideally just 5. Then work up to 4 groups of that as soon as you can.

I started doing this again this week because I hit a real low point that observers may think is depression. I was to the point of feeling there was no reason to get out of bed. That was new for me. It was painful. My sleep was lousier than ever. Then I found out that growth hormone (which is also produced by intense exercise) helps sleep and that insomnia and depression can become a vicious cycle. This motivated me to act, when I understood that going back to heavy lifting (heavy for me, that is, not for a serious jock) would both help me sleep and get me out of the funk.

Take a chance. Throw the dice. Imagine the possibilities. Google neurotransmitters and sleep or neurotransmitters and depression or whatever. Googling doesn't take much effort, but the info could open up possibilities. This is the site I personally found helpful. Your choices may be completely different:

Neurotransmitters and Sleep Regulation

Today I did four sets of five deadlifts (70 pounds sounds wimpy, but I'm a female over 50, and it was good enough for me starting back into it) and four sets of a couple other things with machines we have in the gym. I feel unusually happy. It doesn't solve everything, but it's way better than feeling like crying and staying in bed.

Good luck finding some motivation! And, yeah, beating yourself up about it is not a constructive approach, so don't go there.