Mine went down to almost zero for a straight six month period due to stress and depression.

Now everything is mostly back to normal, but I notice I go through definite up and down periods. Like it can be really high for a few weeks, and then really low again... and then really high. For no real reason. it's just... not there? And not in that frustrating can't get into it even though you want to way, but like it just won't even cross my mind. It's very strange and sort of new for me. but then again I have been under a lot of stress.. that stress level just feels standard now so idk.