 Okay, well, part of it is how you feel. And one of the things, Chris, is being tired for no apparent reason. Okay. But on the reverse side of that, I've seen that a lack of vitamin D affects your sleep. Okay, another big sign is that your bones ache. Now, there's a lot of people listening who've been diagnosed with osteoporosis, which is a thinning of the bone. But again, a vitamin D deficiency. A big one is muscle weakness. So you try to get up from a couch.