query execution time

Hello, everybody

recently I have found that queries on our customer database take longer to
execute than normally.

First thing we did was to log long queries. This led to nothing as queries
logged are usually executed fast. On the other hand sometimes they take
considerable amount of time... Then we tried using EXPLAIN ANALYZE - that
brings me to the question:
"Total runtime" of the query provided by the EXPLAIN ANALYZE is 0.200ms, but
the result of it comes after sometimes 0.2, sometimes 5 seconds. We use
pgAdmin tool to query the DB - it shows how long the query took to execute.
The question is why the difference of value provided by EXPLAIN ANALYZE and
observed one is so big? I know explain analyze has its overheads, but query
itself takes long to execute. Also we've checked if the internet traffic is
not too high - it appears not even close... Now I have run out of ideas what
to check... Can you give me a hint what else can cause such behavior ?

Thank You in advance.]

Julius Tuskenis