This is probably caused by that spear and shield putting you overweight(amazing since wood is so light, you would have had to be carrying an unimaginably huge load(~10000r) already), or something else(a leg or foot injury causing you to lay down) that caused your speed to drop dramatically. Remember that the average speed, and overall speed range, of elves is higher than for other creatures. With your speed being reduced, and a good number of them moving at normal speed(for elves) to intercept you, your computer must update each of their position's 2 or three times for every 1 time it updates yours. This causes tremendous lag as that's a lot of stuff happening around you, where normally each frame only needs about a third of the work. What does the speed counter in the bottom right say? 1100-1300 is average and would rule out this scenario unless there was an amazing number of elves.
I have seen several cases of my own which seem to quite simply be localized site-data-bloat causing huge lag, as if it were some game error, when I walk into an abandoned fortress that should have only had 10-15 olm-men and such in it, on an un-hindered, un-injured adventurer. Save game bloat makes a good bug report, but you have to have an example, specifically the size of the file before starting an adventure, which means writing down the file size of all your saves after each time you save it like some sort of crazy, and showing an example of normal play through adventure mode, and of the supposed bloated file, to actually determine if that's what's going on.