You may find yourself in a situation where Postgres decides to stop responding after an Alter or Drop command was given in PGAdmin. This can be corrected by using the following commands below.
Shell into Postgres:
Select data from the pg_stat_activity table.
SELECT pid, now() - pg_stat_activity.query_start AS duration, query, state FROM pg_stat_activity WHERE (now() - pg_stat_activity.query_start) > interval '5 minutes';
Kill the zombie process after getting the PID exit Postgres and run:
sudo kill -9 <ProcessID>