firstly, I'm sure there is a number of tips re motivation on this sub-forum, so I'd suggest typing in the word 'motivation' into the search facility.
Secondly, 22k is a novella, and it seems to me, that there is a resurgence of interest in this manuscript length - check out the Grinder or similar. The Novella is a well regarded category in many major writing awards.
Thirdly, practically every writer has difficulty with the ending of a piece, because it generally needs to bring a lot of components together - the central idea, the emotional resolution, the plot resolution etc. So that's fairly standard. These end chapters tend to be heavily tied to motivation, so your issue is common enough.
Fourthly, motivation is derived from different elements, as mentioned eg, clarity of the central idea resolution, emotional excitement, and so forth.
so I'd suggest taking time to remember your initial excitement/ concept/ image which started the work, and to spend a bit of time 're-cognizing' ( and re-imagining that initial moment(s).
ETA: Actually Sc, this may be the wrong forum for your post. I'd suggest PM-ing one of the mods to place it in the right forum - I'm not sure exactly which one myself offhand. You'll get more response then.
