Although page breaks are typically not allowed after \subsection commands, I am running into one with the ExPex package. If anyone knows that package specifically, a specific question would be welcome. I'm also interested in any more general solution, however, which would perhaps cover many cases where I'm not sure what's in the macro.
For the time being I am putting everything in a minipage; it feels like there should be a better way to do it, though.
\documentclass[10pt]{book}
\usepackage{expex,lipsum}
\begin{document}
\lipsum[1-4]\lipsum[4]
\subsection{My heading}
\ex
\begingl
\gla Lorem ipsum dolor sit amet, consectetuer adipiscing elit. Nam consectetuer mollis dolor. Quisque malesuada nulla sed pede volutpat pulvinar. Aliquam metus. Morbi turpis arcu, egestas congue, condimentum quis, tristique cursus, leo. //
\endgl
\xe
\end{document}