After not taking Seroquel?

Hi, Patient!
Did you stop the medication abruptly or taper down over several weeks? It sounds like you're probably having withdrawal symptoms. 600mg/day is a pretty hefty dosage and it may take your system time to re-adjust to not having the drug.
Here are some classic symptoms:
"Physical symptoms of withdrawal from Seroquel​ can include:
Nausea or vomiting
Headaches
Dizziness or lightheadedness
Fatigue
Sweating or chills
Restlessness or tremors
Emotional symptoms of withdrawal from Seroquel​ can include:
Anxiety
Irritability or agitation
Insomnia or disturbed sleep patterns
Depression
Mood swings
Difficulty concentrating
Suicidal thoughts

"The timeline for Seroquel withdrawal widely varies from one person to the next. For some people, symptoms might begin within 24 to 48 hours after stopping the medication and last for a few days to a week. For others, the effects can go on for several weeks, especially for long-term users or someone on a higher dose treatment."

Report this to your doctor and get their professional advice as to how to proceed.
Regards and I hope you get through this quickly.
Wildcat