I believe I took my evening meds twice in the past, despite having a pill box. I wasn't as worried about my Seroquel XR, which would have been much higher dose than yours, but my Tegretol XR. I take a huge dose of that anyway, doubling my evening dose was a bit worrisome. I feared double vision. Anyway, rather than worrying, consider calling a pharmacist to ask how concerned you should be.

The worst case of medication taking mistake was by my husband. Instead of taking his meds (antidepressant, stimulant) he took my evening meds instead by accident. He made it to work, but his work friend had to call me to pick him up. He totally passed out almost, sleeping the whole day away.

The scariest thing I experienced was mixing my meds with too much alcohol. My husband had to call 911.