Weird tingling/cold sensation in back, neck and head…is this normal??? i’m also feeling apathy, like not happy and not sad just kinda meh??? any thoughts??

i started zoloft 1 week ago today, im only taking half of a 25mg pill, so 12.5mg. i’m supposed to start going up to a whole pill tmr, but i kinda just wanna stay on half a pill because it effects me so strongly! the nausea i was feeling has subsided significantly, but now i have this almost constant tingling and cool feeling sensation in my head, neck and back. it kinda feels like when you have icy hot or bio freeze on if that helps!! is this normal??? i’ve been feeling it for 2 days now. Also, starting today i think i’m feeling apathetic. i’m not happy but i’m also not sad and i just don’t feel like doing anything, is this also normal??? any advice would put my mind at ease!