Necessity of y-axis label on a line graph?

I'm currently designing a line graph to provide a relative, "quick-glance" view of data trends, rather than the granular stock-market-style view. There will only be one trend line.

Currently each of the data points will be labeled with their y-values. The x-value will be linear units of time.

If the maximum y-value data point will be aligned with the top of the graph, is it okay to only show the x-axis label on the bottom?