"I haven't really searched for (professional) help." Are you planning to get this kind of help? I see no professional way of raising the subject while at the same time making it clear you're not planning on trying to resolve it...

You and everyone else has bad days, one mark of the professional is not to let it interfere with your work or impact on your dealings with others in terms of your work.

Could this be "burn-out"? As a programmer, if this happened to me only every 2-3 weeks, I'd feel like I was winning. Solving tricky, intractable problems can leave me feeling very deflated a couple of days later, and on those days I don't achieve much at all. I don't consider this to be to the detriment of productivity, it's just something that happens from time to time and it's a price I pay for intense mental stress. This ebb-and-flow of productivity is surprisingly common. A good IT manager will be aware that some programmers go through this.

@Kilisi I think it really depends on what is going on. Normal style bad days are things a professional should be able to handle, but if there is something worse going on, it may be beyond normal coping skills. If that is the case, OP needs to see a professional to determine what is going on.

@Kilisi this is dangerous and bad advice, albeit well intentions

@Lawtonfogle I'm not saying they shouldn't, it's certainly an option worth considering..... just don't involve work... colleagues and manager are unlikely to be the pro help needed if the OP decides in that direction. There is no plus side to telling them you're 'mental, likely to get aggressive over nothing and want them to accommodate any outbursts or shortfalls in your work. Especially when it's unsubstantiated. The OP is not asking if they should see a pro, they're asking if they should tell colleagues and manager.... I'm advising against it.

While you should seek help, I think good managers realize that people aren't always productive every day, all the time.

Have you tried doing something to make yourself feel better (as in in the morning of any of such days, or just to generally improve your state of mind)? My top recommendation would probably be some exercise, alternatively anything you enjoy might work. If that doesn't work, I'd also recommend professional help.

@spender: Unfortunately, it's more common than good IT managers.

Gender might offer further context.

Does your work allow you to use your sick days as mental health days? Would they know if you did?

When you say "almost no work done", what kind of work are you talking about? Anything and everything, or just bugs/feature work that involves code? (Planning/documentation/bug investigation (without yet fixing it) are other things that come to mind, that I do when I get in similar moods)

A day off due to poor mental health is a sick day, companies don't generally get to decide whether something is "good enough" to be a legitimate sickness.

Welcome to IT! :P That's kinda commong among software developers. IT manages to combine the worst aspects of any criativity-based work: we need to deliver new ideas on schedule, those ideas must be future proof, they rarely get recognized as nice ideas and, worse of all, we can't drink while we work our art. And we somehow still love it. Go figure.

This doesn't sound any difference to a hangover, very common to have a hanging day now and again where you do sod all but procrastination, at least UK no one makes a big deal about it unless it's too regular.. I don't think you need to draw attention to it, PMs are well aware that they won't get 100% out of everyone everyday