I had a beer 7 hours ago. Will I get sick if I start my Flagyl?

There are 2 alcohol/food/lifestyle interactions with Flagyl (metronidazole) which include:

Major
metroNIDAZOLE ↔ food
Major Food Interaction

Consumption of alcoholic beverages or products containing alcohol or propylene glycol during treatment with metroNIDAZOLE is not recommended. Doing so may occasionally trigger a reaction in some patients similar to the disulfiram reaction, which includes unpleasant effects such as flushing, throbbing in head and neck, throbbing headache, difficulty breathing, nausea, vomiting, sweating, thirst, chest pain, rapid heartbeat, palpitation, low blood pressure, dizziness, lightheadedness, blurred vision, and confusion. Rarely, more severe reactions may include abnormal heart rhythm, heart attack, heart failure, unconsciousness, convulsions, and even death. Patients treated with metroNIDAZOLE should continue to avoid using any products containing alcohol or propylene glycol for at least 3 days until after completion of therapy. Talk to your doctor or pharmacist if you have questions on how to take this or other medications you are prescribed. It is important to tell your doctor about all other medications you use, including vitamins and herbs. Do not stop using any medications without first talking to your doctor.

https://www.drugs.com/food-interactions/metronidazole,flagyl.html

Do not drink alcohol or consume food or medicines that contain propylene glycol while you are taking Flagyl. You may have unpleasant side effects such as headaches, stomach cramps, nausea, vomiting, and flushing (warmth, redness, or tingly feeling).

Avoid alcohol or propylene glycol for at least 3 days after you stop taking metronidazole. Check the labels of any medicines or food products you use to make sure they do not contain alcohol or propylene glycol.

Antibiotic medicines can cause diarrhea, which may be a sign of a new infection. If you have diarrhea that is watery or bloody, call your doctor. Do not use anti-diarrhea medicine unless your doctor tells you to.

https://www.drugs.com/flagyl.html

I suggest you at least wait 24 hours.-