i go to yoga [ashtanga vinyasa] once a week or once every other week. it feels great right after, but either the next day or the second day i generally feel pretty sore. if i really pushed myself, that soreness will last two days. and that's been the case for the past decade that i have been doing yoga. i generally don't do any strength training for two days after and if i go for a run, it's a shorter one at an easy pace.
half sick all week says that something isn't right. it could be that you're actually getting sick. it could be that you're pushing yourself too hard during your yoga videos. it could be that you aren't giving your body enough time to rest after yoga. if could be you doing something wrong or irritating your body in some way by doing a certain pose. i am sure it could be ten other things that i didn't think of off the top of my head.
i will say that i don't so much love yoga videos. it's hard to know if you are actually in the right pose or not. i mean, let's take downward dog. if you're watching a rodney yee video and are doing what he does, you're going to try and keep your feet flat on the floor and likely sacrifice having a straight back, which is the point of the pose. which, if you do in a class, the instructor will likely get you to get your heels up off the floor. now, if you are doing that downward dog at home, you'll likely feel just fine in a vaguely triangleish position. but when an instructor adjusts you to have the straight back it feels a lot better and you start to wonder what it was you were doing before that felt just fine. and even though you're not supposed to look around during your class, if your yoga place is anything like mine maybe 5 people out of 30-40 can have flat feet and a straight back in that pose. and i will say that i have never seen a video that does as good of a warm up as an actual class. the [admittedly limited] ones that i have seen go light on the warming up a little heavier on the complicated poses, which basically means you're a little less warmed up when you're trying to do more complicated things, which makes them harder to do.
the other added benefit of going to a class is that you can ask your instructor if you feel weird after. you can go in the next week and say my x really hurt last week and you can get a modification to just about every pose.
-google first. ask questions later.