Depression has physical triggers. It's not all about how you think and feel mntally and emotionally. While we don't completely understand all the reason why we need ot sleep, sleep is critical to mental health. Ther'e no question. During sleep our brains "reset" chemically after the stresses of being awake and conscious. Two critical things we do know about is that the brains regenerates its stores of serotonin which get depleted during the day, and the brain produces melatonin, a chemical which improves the quality of our sleep although we're not sure how. One simple speculation is that melatonin helps our brain recover from the day on a deeper, more fundamental level as it's link to deep sleep.
Naps can help the body regulate serotonin depletion, while only regular deep sleep produces melatonin. People who have a history of depression frequently have irregular sleeping patterns that disrupt one or both of these processes, and this can trigger depressive episodes. You in fact become more phsyicall fragile and tire easily, and then bam! the depression kicks in (yeah, been there done that). The problem is once these chemical start getting off balance, they effect all of your physical health, including your ability to sleep well. Then you fail to get the sleep you need to recover from the imbalance, and thus a pretty nasty cycle is born. For things like this I can advocate the use of SSRIs. I was in this cycle myself and ended up barely sleeping at all and thinking about suicide compulsively nonstop. I took Zoloft for 18 months and got a lot of rest. Things are a lot better now.
I understand that you are or were getting professional help for certain matters, but I do not knwo if you are on any SSRIs. If not you may want to consider it as an aid to get you back in a better physical state so to better manage your depression overall. If you are taking a SSRI, then you should talk to your doctor about changing dosage or meds. You probably also need to look seriously at what else you can do for your physical health. Do you get regular sleep, at least 5 hours of it at roughly the same time of day every day? Are you eating right? Are you getting enough protein, vitamins, minerals, omega 3 fatty acids and other healthy fats, and antioxidants? Do you drink enough water to help your body eliminate toxic byproducts of metabolism and stress? Do you get enough physical activity or exercise? That last one's very important. Regular exercise also helps the body regulate serotonin depletion and restoration, and encourages better and more regular sleeping pattern so your brain makes enough melatonin. Exercise also helps eliminate toxins from the body, which can be another physical trigger of depression.
I have personally found that you can't just do one or two things and think that's enough to maange depression. Depression is a complete package - it effects us mentally, emoitonally, spiritually and physically. In order to most effectively manage it we have to touch on all those bases. At the start or your recovery, you should strive to tackle one problem at a time, and normally that does get positive results, but only short term. As you progress in your recovery you have to continuely develop a more sophisticated plan to manage your depression long-term.