When my girlfriend was a surgical trainee, she often felt dizzy and even nauseous during long early morning operations.

Her surgical mentor — who is still a dear friend — asked what her breakfast choice was. (Answer: “one toast with strawberry jam, and two cups of tea.”) He then taught her a valuable lesson by explaining that the sugars in the strawberry jam gave her an early energy boost, but that the boost didn’t last long enough. So he suggested a compromise:
“Eat your strawberry jam toast with two extra layers of your typical Dutch Gouda-like yellow cheese, and you’ll be fine.”
And she was (and still often follows his suggestion).
As for your question: oatmeal actually is really healthy for breakfast — it is rich in fibers, vitamines and carbs — but it lacks the kind of energy you would need for long mornings.
So don’t stop eating the oatmeal, but add a toast with one or two layers of young yellow cheese —
And you will be just fine.

A package of instant oatmeal can be about 1/3 simple sugar (~12g in 41g). There are healthier options.
The kind of food you want to break your fast, when your insulin levels are at their lowest and therefore prone to blood sugar spikes, is something that is rich in fiber.
Oatmeal, by itself, is actually a great option since it is a rich source of fiber. Fiber is key in moderating carb absorption. When combined with complex carbs, your body is provided with enduring energy throughout your day, without spiking your blood sugar level.
What makes oatmeal special is the rare type of soluble fiber in it called beta glucan, which is known for many health benefits, including:
- Lowering blood cholesterol
- Reducing blood sugar
- Weight reduction
- Boosting the immune system
- Reducing the risk of obesity
- Reducing insulin resistance
- Reducing the risk of metabolic syndrome
Foods that offer the most beta glucan are oats and barley. It’s recommended that you get 3g a day, which takes 1.5–2 cups of cooked oatmeal (50-75g uncooked).
95% of the US population does not get enough fiber. It’s recommended that adult women consume 25g of fiber a day, and adult men 38g. Not getting enough fiber is a big reason why the above health issues (diabetes, heart disease, bowel-related disease) are so widespread.

^ There’s ~1g of fiber for every 10g of dry oats. For comparison, a 150g potato has 2.2g of fiber with skin, and half that without skin (e.g. hash brown).
In contrast, a breakfast full of proteins and fats, such as bacon/sausage and eggs, makes your gut feel heavy and requires much more blood to digest, taking away from blood available to your body for physical activity, greatly stunting your aerobic efforts.
Competing athletes are advised to give scrambled eggs at least 2 hours to digest before an event. The advice that you shouldn’t swim after eating originates from these facts, as you can imagine the consequences when a swimmer makes a risky decision that calls for their peak performance to pull off.
What makes oatmeal questionable is that raw oats, like many other grains [and raw seeds], have phytic acid, which has a temporary “anti-nutrient” effect. It binds to minerals like iron, zinc, magnesium, and calcium, reducing their absorption in the digestive tract. Cooking removes only 10–20% of it.
To counter it, you can either remove it through methods like soaking overnight (AKA overnight oats, which gives it a creamier texture), treat the oatmeal as a complete meal by itself (rely on lunch and dinner for micronutrients), consume more of these minerals (perhaps through enriched foods), and/or consume oatmeal with foods with vitamin-C (e.g. fruits and berries), which that enhance mineral absorption.

There are many easy recipes for overnight oats that can counter much of the anti-nutrient effect, as yogurt and acids in fruit (even better if you add lemon juice) can break down the phytic acid. Adding wheat or rye (even in flour form) can add more phytase (activated by soaking), which directly counters the phytic acid. You can safely do meal prep for many days in advance with these ingredients.
While this may sound scary, what’s most important is that you have conscious control over what you eat, and follow wise guidance. You know all those sayings that “moderation is key”? Ask yourself, what is key to moderation? It’s self-control/discipline.
It’s absolutely no surprise that people who can exhibit enough self-control can be part of the mindful crowd, compared to the preference-driven crowd who follow their urges and who are often swayed by biases.
Preference-driven types rely on their choice of copium, usually some addiction like nicotine, alcohol, gambling/gaming, collection of nonsense things (when hobbies turn into hoarding), comfort foods, etc. to cope with the stress of continuously ending up with less than ideal circumstances.
Being told that all these things are bad only gets them to come up with nonsense to counter the “good/wise/healthy” alternatives they’re recommended, as a way to mitigate the amount of guilt they feel.

^ Jennifer Aniston adds an egg white to her oatmeal right at the end of cooking for extra protein.

^ Hafþór Júlíus Björnsson (The Mountain) says that you make champions by being consistent, enjoying 200g of oatmeal as part of his typical breakfast.
If you’re a type who giggles or is embarrassed about the thought that fiber makes you poop, or is for constipation, perhaps you’re due some poop trivia.

Personally, I eat a relatively filling breakfast and skip dinner.

^ walnuts, sunflower seeds, and a dollop of yogurt in my oatmeal. The walnuts and sunflower seeds are for a balance of omega-3 and omega-6. It might be strange to have salad for breakfast, but I’m willing to go against convention to get my daily needs of fiber and micronutrients. It’s my priority to be concerned about these things, and minimally about protein, carbs, and/or other macros.
I don’t follow any specific diet—I just aim for more complete nutrition, hoping that a good variety that avoids empty calories (foods that lack minerals, vitamins, and fiber) meets my goal without excessive calories or hunger.
I reserve the right to delete comments full of disinformation—mostly the paleo/carnivore pseudoscience comments that are no better than flat earth comments that basically just simply state the planet isn’t round. People who monitor blood glucose levels evidently read 120–140 at breakfast on a keto diet, and 135 for an oatmeal breakfast for average people.
Anything less than 180 mg/dL within 2 hours of eating is generally fine. Keto’s fine, and shouldn’t be confused with carnivore diets—they’re generally a little under 100 for the rest of the day, after their insulin does some work.
Instant oats evidently spikes to 200, due to the refined sugar. Whole fruits have fiber in them, so they’re not a bad source of sugar either—fruit juice is worth cutting out, though.
Endocrinologists, specialists who are qualified to treat diabetes, metabolic disease, and other diseases related to the endocrine systems (irregular heart beat, weight, fatigue) say oatmeal is great and beneficial to the body.