Re-enter interactive mode after Ctrl-z

type fg and hit enter in terminal.

   fg [jobspec]
          Resume jobspec in the foreground, and make
          it  the  current  job.   If jobspec is not
          present, the shell’s notion of the current
          job  is used.  The return value is that of
          the command placed into the foreground, or
          failure  if  run  when job control is dis-
          abled  or,  when  run  with  job   control
          enabled,  if  jobspec  does  not specify a
          valid job or jobspec specifies a job  that
          was started without job control.

Type the following to pull the job to the foreground again:

fg

This is because you suspended the job, meaning it's doing nothing while you can't see it. You can actually let a job run in the background too (by entering bg). See Job Control for more info.

You can use fg to bring the foreground activity back

OR

You can use bg to move the current activity to background.