Help. My peppermint essential oil is crystalised and I can't get it out of the bottle.

Depending on how cold and solid the oil is, there are a couple of ways to do this.

The most gentle way to warm up your peppermint essential oil is to warm the bottle in your hands. You can even tuck it down your bra or somewhere that it will be against your skin. Let our bodies natural warmth heat it up. Please ensure the lid is on securely and there are no spillages on the outside of the bottle as essential oils should not be put on the skin neat (undiluted). If you do happen to accidentally spill it on your skin neat, do not wash it off with water. The first thing you need to do is to dilute it with a carrier oil. You can use fractionated coconut oil or jojoba oil if you have it handy. If you don't, walk to the pantry and grab a bottle of olive oil or anything you have on hand.

The quicker way to warm up your peppermint essential oil is to run the bottle under warm water. Again, ensure the lid is on tight as you don't want to dilute your essential oil with tap water. If you don't like this being wasteful, get a glass and put warm water in the glass and let the bottle float in it.

Regardless of which method you choose, let the bottle get warm and swirl it until you get the desired effect - ie: a liquid state again.

It doesn't matter if it's a cheap brand or an expensive one, all peppermint essential oil has the capacity to do this.

No. It's not a good idea. Peppermint is very high in menthol. It's very cooling which is why it's used in foot lotions and foot soaks a lot. Since feet overheat easily, the peppermint oil cools them down. But it must always be diluted. If you don't dilute it enough or at all, the cooling effect will be very uncomfortable and possibly painful. Even diluted, diffusing peppermint essential oil for long periods of time can make you feel cool inside, which is not a good idea.