There will come a point in every introverts life when they just don't wanna. My response to those times is "then don't."
Seriously, there is almost nothing worse than being with people when all you really want is to be alone in your bed with Netflix. Sometimes you need those days. Now if you have a long standing string of don't wannas, then you have something going on that needs to be addressed. The occassional, end of the week, I'm just done with people moment happens, go be by yourself. If anyone harasses you about it, tell them you ate something funny at lunch (note to self, always eat a joke at lunch time so as not to lie to people). It is acceptable and expected that introverts will need time alone, don't feel inferior that you're not out with your friends every night of the week. That's the fast track to hating yourself and your friends in introvert land.
Now, what if you've already said yes and it's at your house and people are on their way and your house is a disaster and there is not a single food prepared. Take five minutes to dump everything off your eating space table, take another five minutes to order several pizzas or Chinese delivery and then go hide in your bedroom until a doorbell rings. Hopefully, it's your favorite person in the world. But more than likely it will be that first, last friend (the friend that shows up first and leaves last, we'll talk more about them later). Give that person something to do, like putting out paper plates and napkins or going to the garage for that dusty twelve pack you've been harboring. Hide a little longer in the bathroom, cleaning the toilet while they do that. People should start to trickle in and by this point, either you can do it, or you should continue to hide in your home doing busy work hosting until they're gone.
Not every gathering has to be the best! You're not having folks over to show them your mad homemaking skillz, yo! It's just for time together. And sometimes you can do more than you think you can. I don't think you should push yourself to be with people all the time, just sometimes. And at the same time, I find it perfectly acceptable to say no to invitations from others just so you can lay on your couch in your pjs. This is your life, you need to take turns being pushed and retreating. Introverts may need more of the latter than extroverts but that's what makes the world interesting, our differences.
At the end of the day, when you don't wanna, then don't. Unless you always don't wanna, then you should broker a deal with yourself to give it a try anyway.