Weakness and Increased Heart Rate

I'm 6w4d and morning sickness (around the clock) hit last week in full force. I expected this, but I didn't expect to feel so fatigued. My heart rate shoots up into the 100's just trying to dry off after a shower. I get lightheaded after climbing the stairs or moving too much. I'm down almost 10 lbs, but I'm still able to eat small meals and drink water all day, so I know I'm not dehydrated. Has anyone else felt this way? Non of this accompanied my morning sickness in my first pregnancy, but I was severely dehydrated in that pregnancy.