Everyone is energized. Strap on, put it the fires. If you did your architecture right (e.g. put it somewhere like AWS), scaling up the servers is no problem.
We were so energized that we built the whole customer management system in one day, something that takes others weeks to build.
If this is happening, customers usually need whatever you're selling and are much more fault tolerant. At peak, we had 10 crashed a day per user. But it was a good sign that they kept logging on despite the crashes. If you have too many customers to handle, a rule of thumb is to deal with the latest ones first because you've likely already lost the ones who were in the queue for a week.
The biggest threat IMO is that you can actually overestimate yourself. We tried to push at a valuation that is too high, because we got our hockey stick early, but it was much more than investors were willing to take.