it's "draining" because men are supposed to be "weakened" by it. it's why women can cum one after the other without having much, if any, downtime...while most men have "downtime" after having an orgasm..and why a lot of men sleep after sex. if men weren't like that you women would never leave the bedroom.
In tantra you are supposed to go for long times without ever ejaculating in order to build your chi without draining any of it. Masturbation is defiantly draining your bioenergy in certain ways, but it depends on the circumstances to whether that is harmful or not. If you only masturbate or ejaculate once in awhile then its fine. If you have a bunch of built up energy then it is good to release some, it will center you. But if you masturbate once a day or more, then this could be harmful to your health. Not extremely harmful, you will just be really lethargic and unmotivated from loss of energy. I know if I go on little fappin biinges I can't even make it out of the house later in the day. Try waking it like twice a day for 3 days and you'll feel so tired and weak. It depends on you do it, and how long you do it, and how long its been since you did it, etc etc. Sometimes you want to go to sleep afterwards, sometimes you just feel refreshed and would like to go for a walk or eat food. Either way if you ejaculate and orgasm there is energy being released in that orgasm, thats basically what a orgasm is, some kind of kaskading release of energy.
For me I say emotionally stimulating. It feels great, especially if you do it with a partner, it makes me think of new ways to do it and to enjoy it. I love it. No, not draining for me.
Quite the opposite for me, I always feel more alert and energetic after masturbating, it actually takes longer for me to get to sleep after cumming.