That sounds like hypoglycemia. Your blood sugar probably dropped on you. A small glass of juice and peanut butter/protein will bring your blood glucose up. The protein is important to stabilize your sugar. You might want to get a blood sugar monitor (glucometer) from the drug store. They are fairly cheap. If this happens frequently you should talk to your doctor before continuing this particular diet. You don't want to start passing out or worse.

Your muscles (heart included) needs potassium to function properly. The Keto diet you have troubles keeping electrolytes up and have difficultly getting some electrolytes (like potassium)

If you have low potassium you heart will often palpate. You should get the seasoning salt lite (half NaCl/half KCl) or NoSalt (All KCl). You should also get a magnesium supplement because the body cannot put to use potassium without magnesium. Magnesium is another electrolyte that can be difficult to get on this diet. Look for a magnesium supplement that end in "ate" magnesium oxide is less useful.

Edit: NUUN is also useful for this, it is a sugar free electrolyte tablet that you drop into water. It fizzes like an alka seltzer.

I take prenatal vitamin. Should I also take magnesium supplement apart from that? Will making 2 cups of broth with lots of salt suffice for getting enough electrolyte?

Multi-vitamins as far as I know have no electrolytes in them. Prenatal vitamins only add/increase a few things like iron and folic acid. So yes you should look at something in addition to that.

Broth is a great way to increase your Sodium. You will have to check if your contains Potassium in it, or add it yourself. You can customize MFP to add Sodium and Potassium to your diary, or view it under nutrition in the App. It will be in mg so keep that in mind. But Kiramaniac's 3-5g of each is a good place to aim.

I am new to this diet as well (4 days in) and drink something called Sole water. It is made with Himalayan sea salt and it is great. Not all salt is created equal! I have not had any side effects at all, Keto Flu or otherwise and I really do attribute it to this drink.
http://wellnessmama.com/12158/make-sole/

Sounds like a potassium deficiency - extremely common on Keto. Get yourself some potassium salt (called no salt) and use 1/2 tsp a day for a big boost to your potassium level. Same thing happened to me and occasionally still happens when I get lazy.

I encourage anyone to make beef or chicken bone broth. The internets have tons of recipes. Good minerals and other compounds and much better than the instant broths...

Your muscles (heart included) needs potassium to function properly. The Keto diet you have troubles keeping electrolytes up and have difficultly getting some electrolytes (like potassium)

If you have low potassium you heart will often palpate. You should get the seasoning salt lite (half NaCl/half KCl) or NoSalt (All KCl). You should also get a magnesium supplement because the body cannot put to use potassium without magnesium. Magnesium is another electrolyte that can be difficult to get on this diet. Look for a magnesium supplement that end in "ate" magnesium oxide is less useful.

Edit: NUUN is also useful for this, it is a sugar free electrolyte tablet that you drop into water. It fizzes like an alka seltzer.

^^^THIS^^^ (Or it could be low blood sugar as one poster has suggested, but, just guessing it is your electrolytes being off balance--which can be dangerous.) It would be a good idea to track your sodium and potassium. I have entered a bunch of foods in the data base under the label "(corrected for potassium)" . The average healthy active female should aim for 3,500 mg. of potassium per day (for men, it is around 4,000 or more, depending on how big they are). Most days, I make my 3,500 mg. and I feel a lot better for it. I eat "lower carb" rather than "low carb" because the ketogenic diet causes me to dump too many minerals. Vegetables (and fruit to a lesser degree) are VERY important for raising your mineral levels. White potatoes (which are usually a dieting no-no) are EXCELLENT for raising potassium levels (and magnesium as well). Foods that are high in potassium are almost always high in magnesium as well. So if you track and meet your potassium target, you can be assured that your magnesium goals are being met. Sodium and calcium are antagonistic to meeting potassium and magnesium targets (excessive sodium works against potassium and excessive calcium works against magnesium). You should aim for getting about half as much sodium as potassium. The situation with calcium/magnesium is just reversed--you should aim for getting about half as much magnesium as calcium. The normal appetite usually causes us to desire foods that keep our mineral levels at optimum. But, when you diet, you are necessarily restricting something and it could be something that your body needs. That is why large calorie deficits day after day are dangerous over time. Anorexics who die, typically die because they have injured one or more organs with large calorie deficits and it throws their electrolytes completely out of kilter.

ETA: I have found that the sodium levels in processed food and restaurant food is SO HIGH that eating it makes it quite impossible for me to meet my targets. I would be leery of potassium supplements unless your potassium levels are being monitored by a doctor. Minerals are perfectly balanced in vegetables which are salted to taste with ordinary table salt. (Sometimes our taste for salt is exaggerated from years of eating too much salt, though.)