Where is the money that was in the economy pre-lockdown? Countries are in lockdown, companies have no customers and thus no income. 

They have to lay off staff which in turn means ex-staff have no income. Everyone simultaneously and quickly depletes any savings so they can no longer buy goods and services. 

Where is the money that was circulating in the economy before lockdown?
A very insightful question. The thing I'll add here is the famous identity, MV=PQ. Essentially you're asking why Q dropped (real goods &amp; services), while M (money supply) likely is the same. There are (at least) two answers: 


V (Velocity) could have dropped - which has the same effect as shrinking M. $100 making 10 round trips is very different from $100 making only 1 round trip. 
More nuancedly (sp?) - You could be seeing a collapse in the "composition" of the Money Supply. I.e. Maybe M2 collapsed back into M1, etc. If lots of people called in their loans (M2+) &amp; converted to cash (M0), the same amount of money might be there...but it would have been "sucked" from the system, in a sense.