I was getting about 40 miles to the gallon but all of a sudden I may get 20 mpg. on 1995 Toyota Camry

I took my car to a mechanic just to glance at and they said transmission and motor both sounds good. Not leaking anywhere either so I am so confused???

Asked by for the 1995 Toyota Camry
Has got to be a noticeable difference in performance for mpg to be cut in half!! Sure about 40 mpg? What engine? What transmission, automatic or stick, some were manual shift.
1 more answer
Is the check engine light on?