Insomma needn't keep you up at night: it's not insomnia (insonnia), just a common phrase you'll hear Italians use a couple of different ways.
Its primary definition is all in all, in other words, in short – like a much more conversational version of 'in sum'. Think of it a bit like the way we've come to say 'basically' in English.
Era sporco, scomodo e caro – insomma un disastro!
It was dirty, uncomfortable and expensive – all in all, a disaster!
Abbiamo bisogno, insomma, del buon senso.
What we need, in other words, is common sense.
Mi piacciono molto le lasagne alla bolognese, ma anche quelle alla genovese o alle verdure; insomma mi piacciono tutte.
I really like lasagne bolognese, but also pesto or vegetable lasagne; basically I like them all.
And like 'basically', insomma also acts as a kind of verbal filler you can use when you want to move the conversation along – like saying 'well' or 'so'.
Insomma, siete pronti?
Well, are you ready?
Insomma, cosa ti hanno detto?
So, what did they say to you?
You'll also hear Italians resort to it when they're too exasperated to say much else.
Alright, that's enough!
For goodness' sake!
There's also an unwritten meaning in insomma: in spoken Italian it's come to serve as shorthand for saying you're not too keen on something or that it's just so-so, usually in response to a question.
If you're using the word this way, remember to throw in a laconic shrug or some 'meh' hand gestures.
– Ciao, come stai?
– Hey, how are you?
– Can't complain…
– Ti stai divertendo?
– Are you having fun?