Started Taking Vyvanse this morning, freaking out a bit

I took my first dose of Vyvanse this morning, and man its freaking me out. At work so far there have been long stretches where I don't have an internal monologue (the voice in my head, which has been going for basically my entire life as far as I remmber, is almost entirely absent unless I force myself to think about something). I've been noticing that I'm tensing up and have to actively release my body's tension (like neck, jaw, shoulders, etc). maybe I always did that and im just noticing it? I don't know. My brain feels like its tensing up and releasing itself, like my head is pulsing. My Dr. Proscribed me to take 70 MG to start, i've never taken a medicine for ADHD before ( i didn't/ am not fully convinced I have it, but I trust doctors). Can anyone kind of talk me down a little bit? is this normal? why do i feel like my eyes aren't open wide enough?

EDIT: Thank you everyone for your thoughtful and kind responses. I called my Doctor yesterday evening and explained the issues, and he suggested that I try the reccommended dose 1 more day, and if i still feel this way, to do as you all have suggested and mix the contents of the pill with water and take half a dose. I took half a dose today in stead, because I CANNOT go through that again! You guy's support and messaged helped me ground myself during a really rough time yesterday, and impowered me to not disrgard my reservations. Luckily I'm not working in the office today, so even if I hav eadverse reactiosn I won't also have the paranoia of thinking about what my co-workers are thinking about me as I go through this stuff. As a funny aside, my wife said that I sounded exactly like Eeyore the entire day, until the medicine wore off, which I found funny.

EDIT 2: After 2 days of taking the perscribed dose, I'm now confident that I need to go down (yesterday was better, but Still I was in a really weird spot). I'm now taking half the dose (35mg) by mixing the caplets with water. Thanks everyone for all the support, and empowering me to feel confident enough that I can make this descision for myself. On monday I will call my Dr. as they don't take calls on the weekend unless its a medical emergency.