Missed dose

I've been on effexor rx for years and it's been my miracle drug (i've tried the others but had numerous side-effects).  I take 375 mg's a day w/100 mg trazadone.  The other night I missed a dose and followed the directions to skip it and go back to my schedule...  "If you miss a dose of Effexor XR Extended-Release Capsules, take it as soon as possible. If it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule..."
Well, I been feeling so crappy..the same side effects as those quitting have expressed.  I'm nauseas, tired, and have flu like symptoms.  The last time I missed a dose, I took it as soon as I remembered and then took it again 12 hours later then went back on my normal schedule and I didn't feel this awful.  Now I'm wondering if I should make up this last missed dose?  I think my body is going through withdrawl (withdrawal) and it needs the 375 mg that it would normally function on...  Is this what I should do?

Advise is welcome, please..

Thank you,

G