It can happen at any time, but it's most prevalent when sending off a submission. You're sure you've done everything possible to polish it up, you may have a time limit for that submission, you may already have done one, when you click that "send" button it'll all be over - the submission will be out there and nothing will change that. Your mistake in that submission might prevent you from getting the agent or publisher you so desperately want, that you so painstakingly researched.
Yeah. I've had that. More times than I'm comfortable recalling. Just admitting it like this takes a bit of effort to be honest. It feels like baring my soul. But it's also one of the best ways to deal with it. If someone tells you that you - as a man - must control your emotions, there's only one thing to say. Bollocks! Men have just as much right to fret and be nervous and agitated as women. And consequently we should open up to others and allow them to help, not just bottle them up in some foolish show of idiotic masculine pride.
So what's it like to get submission nerves and niggles? It's terrible. It's like that day when you went on your first trip to the dentist knowing that something was wrong. Or that time you went to the doctor not knowing what they would say about that pain in your ear. It could just be wax, but it could... Basically, it's that feeling of butterflies with razor-edged wings fluttering through your stomach. Or a fairy from Drakengard hissing in your ear. Not pleasant.
It's worse if you also suffer from occasional bouts of depression that rear up for no apparent reason other than to get you down. But I've also got the routine down for dealing with it; take that meaningless depression, wring it into unconsciousness, and push it out the window or into the back of your mind in a lead-lined chest where it belongs. It's just your nerves, and your nerves can be mastered. In fact, doing this makes for some great experience for writing about such attacks of nerves in your own work.
Mind you, this also applies to writing in general. if you want some advice on that, go check out Erica Verillo's post on the subject. Here's a quote for you from that article.
I find that advice more than true. Please, everyone, keep writing if it's what you want to do.If you have doubts, does this mean your beloved novel is a piece of crap, and that you should quit right now before you follow in Franzen's self-loathing footsteps?No, keep writing. And keep revising. And make sure that you've given your finished manuscript to the most critical readers on earth, and that they have drawn blood.
*Nigglewight: A fictional term combining the words 'Niggle' (a word referring to something causing persistent annoyance, discomfort or anxiety) and 'Wight' (an English word originally used to refer to living humans, later to refer to living sentient beings or living creatures, and later to more supernatural and often malevolent sentient beings such as undead or spirits).