Restart tdm after exiting session

[zeronoises]

At the moment I have tdm successfully setup to start either a spectrwm or herbstluftwm session. Right now I find I'm switching frequently between them. Each time I drop from a session, I land back on the tty - obvs - but have to manually restart tdm. I would much prefer to drop to an active tdm - as would be the default behaviour with a graphical dm.

I use zsh: at the end of my .zprofile:

# start tdm

exec /usr/bin/tdm

And my .xinitrc:

#!/bin/sh

if [ -d /etc/X11/xinit/xinitrc.d ] ; then
 for f in /etc/X11/xinit/xinitrc.d/?*.sh ; do
  [ -x "$f" ] && . "$f"
 done
 unset f
fi

exec tdm --xstart --silent

EDIT: to be clear, at the end of each X session I drop back into TTY1 but still logged in - with a screen full of the remains of tdm's activity.