Thanks. However, that post seems to be for getting info from the database -- I'm doing a confirm page before sending it to the DB. Sorry if I wasn't clear. I finally got this to work:
$saForm = '
<input type="checkbox" name="healthConditions[]" value="limiting physical disabilities"';
$saForm .= (in_array("limiting physical disabilities", (array)($_SESSION['healthConditions[]'])) ? "checked" : "");
$saForm .= '
limiting physical disabilities';
echo $saForm;