Sleep deprivation has a well-established anti-depressant effect. Sadly it does not last, the emotional state soon returns to the baseline. The temporary reprieve could push you over the edge though, if you were close to it.
At least according to Matthew Walker, in his Why we Sleep (which I recommend to everyone), it doesn't work for everybody. Only some people get anti-depressant effect.
The risk is people are more likely to commit suicide when they are mildly depressed than severely depressed. In a deep depression you lack the motivation to commit suicide.
That's true, but not specific to sleep deprivation - other methods of easing depression such as SSRI also increase the likelihood of self-harm. I would imagine sports can have similar effect.
My pet theory is that there are several conditions that look like "depression", one of them is produced by the body to prevent self-harm resulting from acute anxiety. This theory has two important consequences:
1) Trying to ease certain kinds of depression via medication or other direct-action tools is likely to cause unintended side-effects (self-harm, anxiety, mania) that the depression was there to prevent.
2) The body will fight back against any direct intervention, trying to reinstate control over unbalanced psyche, e.g. building up tolerance to medication. A more fruitful approach would be to locate and eviscerate the underlying anxiety-inducing problem; the depression should then lift on its own accord.
Like I said, it's just a pet theory, but it leads itself to validation.
