It is no fun feeling blah for no apparent reason.  Maybe what I feel is unique to me - or it is a common human condition.  I don’t know.  All I know is it happens.
Typically, I am going along and all is well.  I can go weeks and months seemingly from strength to strength.  Then one day for no reason I can put a finger on, I am as flat as a pancake. 
It seems at such times I spend time thinking about all the things that are untrue.  All the things that could be misconstrued.  I have heard it said never doubt in the dark what was true in the light.  I hold to that big time, but it does not mean that doubts will not arise in the dark.  Not doubts about my faith, but doubts I know are untrue about my personality and abilities.
To me an analogy I once heard stands true and I appropriate the principle big time.
I read it in a book about how so often a planetary eclipse is like how we are.  In an eclipse one planet can go in front of the other - completely obscuring the light source.  What I read was that often the way I feel can be represented by the dark planet.  I do not deny the feelings I may be experiencing exist, but I do deny they are the totality of who I am.  I am both the dark and light planet with a bridge collapsing behind me while on my journey from the dark to the light planet (that bit is from a song/poem I love, "and everything you are, is making my heart into a bridge from which I may get back from exile, and grown man, and now the bridge is breaking.")
Just because I think something does not make it true.  I reject what destroys and attempts to pull me down.  It was decades ago but I do remember someone saying something that to me is as true today as it was at the time.  “Never make a decision when you are down.” 
Even while not denying the feelings I am having, I know that they alone do not represent who I am.  Who I am and aspire to be is represented by the light planet.   I am confident that all will work out.  That everything is under control.  That what I need to do is hang in there. 
There can be times I know I have not got it wrong, but my feelings will scream at me that I have got it wrong.  There are a few things I hold on to at such times, but it is really reassuring that like an eclipse it will pass.
The sun always shines again, and storms are a part of life.  They are not the time to make changes.  They are the time to hang in there.  Eclipses and storms have a limited life span.

This to me from James Clear seems to make a lot of sense.
“Before you worry about being more productive, think about being more selective. Rather than focusing on increasing productivity, it may be worth asking, "What would I be delighted to spend time on, even if it went slowly?"
Direct your energy toward figuring out how to start what you want to do rather than thinking about how to shorten what you don't want to do."
I appreciate there are times I am not in a position to be selective about things.  Like when I am employed by someone and asked to do a specific job.  Even then I do have a choice but the consequences of failing to do what is asked are huge.  I do remember in the 80’s (1980’s that is and not the 1880’s) wanting to give something away and having a “coming to my senses” moment.  I remember it like it was yesterday.  I saw as clearly as I ever have the ramifications of giving my job away.  I kept the job, and I am very pleased to have dealt with  the offence and come out the other side bruised but better off.
Yet in a volunteer situation I know I am better off doing what I really feel is my strength to do rather than filling gaps because they are there.  I know that as a boss the buck stops with me and in that situation it is very necessary to do what has to be done if I am committed to it.
On the other hand though if I am filling many a role it way better if I am driven by passion rather than necessity.
I have heard someone say “if something needs doing I just get in and do it.”  I know my thinking may be wrong, but I disagreed to their face as I think that is the fastest way to burn out that I know.
I have said it before and I know it may not always be possible but I would rather no one then the wrong person.
I know I am way more likely to do well doing something I am passionate about then something I have just got to do and keen mostly to see it done and dusted as it was never “my thing.”

There is a Latin adage that says, “if there is no wind, row.”
I do like that.  I reckon that once I have established I am heading in the right direction then it makes no difference if there is a good wind blowing me along or I need to row.  Naturally I prefer a good wind, but I have not had to live long (even though I have) to know that life is not all smooth sailing.
At times things seem to be really against me and I need to struggle for what I want (perhaps like bailing in the analogy).  Thankfully that is not always the case or I may be inclined to give up.  But it is a fact of life that sometimes things are against what I know is best for me.
But it seems to me that is a blessing in disguise.  The only way to grow stronger is face and overcome opposition.  I reckon that what I face early, strengthens me for what I face later.  Never sought and never desirable but always beneficial – as long as I let it be.  To me it is really sad to give up perhaps unknowingly just before reaching a goal.
Most goals I want to reach I am encouraged along the way.  It may be just a bit here or there but always enough to help me know I am going the right way, and fortify me for what may lie ahead.  It reminds me of the saying “never doubt in the dark what was true in the light.”  Sort of ties in with another thing I have heard.  “Never make a decision when you are down.”
It is weird but when I am down, I am always tempted to give up on a dream.  Yet it seems to me that is the most important time to hold fast.  To just hang in there. 
I do not want to be someone who talks like their best days are behind them.  I reckon my best days are in front of me.