Yes, you can use quantitative hashtags like #sleep:8hours, or #aspirin:1pill. Note: there should be no spaces between your tag, a colon and a numeric value with a descriptor. You’ll be able to view all records tagged #sleep by tapping the hashtag anywhere in the app (with one exception of record editing screen).
You can see correlation of mood and other things tracked with quantitative hashtags by clicking on chart icon in the upper-left corner of the Summary graph to access a landscape mode.
By using pinch-zoom, scale the chart to a required period of time. Then, pull down the upper menu to see the list of tracked numeric values. On the right, you can see the number of times a #hashtag has been used and its minimum/maximum value.
For instance, it is possible to track depression and hypomania at the same time with iMoodJournal, using quantitative hashtags. Users can assign a level to depression and/or hypomania (as if they used 10-grade scale) and add corresponding hashtags to mood records, for instance, #depression:8lvl and #mania:5lvl. Later, they are able to visualize both graphs representing the level of depression and hypomania against mood graph on the landscape chart. You can assign level to stress, track it and later visualize against mood graph in the same way.