The same as it should feel if you spend your fiat on something other than bitcoins before the price goes up.
When people hear about Lazlo spending 10,000 bitcoins on a pizza back in 2010 they usually say "damn, he's probably kicking himself right now".
Well, why aren't you kicking yourself right now for not buying 10,000 bitcoins for $25 back then? It's the same thing. He could have spent $25 on a pizza or 10,000 bitcoins on a pizza. Or he could have spent $25 on 10,000 bitcoins.
So if you spend some bitcoins on something, then the price goes up. Don't worry about it. Would you have spent fiat on that thing? Fiat that could have been used to buy bitcoins...
this is classic debate on whether bitcoin is an investment or can it be a currency.
for those who see / use bitcoin as another currency it doesn't matter what the price is, like the pizza story. they don't care if the price will go up the next day or falls to the ground because they are spending as they earn.
but for those who see it as an investment and don't see the potential of a currency (at least not yet) it is supper hard to even thinking about spending bitcoin while it can go up and they make huge profit from their investment.