First, that sounds normal, and it's fine to encounter this feeling. Facing unknown challenges is a big part of creating new value.
Next, it's time to take a day and spend some time planning. Bring clarity to what your goals are for the next couple of months. Having a small set of clear priorities, allows you to ruthlessly defer and minimize everything that isn't absolutely necessary. It's less overwhelming to deal with only 1-2 things like this at a time.