Panic arising in meditation

My meditation technique is that of closing my eyes and focusing on the sensation of the breath as it passes in and out of my throat.

What kind of meditation are you doing.Samatha or vippassana?If it's samatha just keep focusing on the physical sensation of the breath.If it's vippassanna just keep noting.

I saw swirling lights in the darkness of my closed eyes. As I became more deeply focused on the breath-sensation, the lights went away and there was darkness, but the odd thing was that the darkness extended- it seemed as though I was looking down an endless, dark hallway rather than just looking at my eyelids.

You may be seeing Phosphenes since you mentioned looking at your eye lids.Also your not supposed to be looking at your eyelids your supposed to be focused on the breath.

As I noted this, I started to see a purple, vibrating orb appear.

This could be the nimitta.But nimitta arising is one thing and leading to a mystical experience which i assume is the jhanas is another thing.Nimittas become quite common when you sit everyday.Sometimes they appear and dissapear when you start breathing.This kind of nimitta is as useless as phosphenes.Don't shift your focus from the breath to the nimitta.In other words.don't try to look at it.It will disappear and appear at another point and you'll spend the rest of the meditation playing tag.

I remember thinking to myself that maybe I was about to have some kind of mystical experience.

If you would like to experience this "mystical experience" ignore the nimitta.The more you ignore the better.Keep your focus on the breath.The nimitta will break into your awareness on it own and merge with the breath,or specifically the point where the physical sensation of the breath is felt.

I became a little excited about this, but all of a sudden the excitement morphed into an incredible fear.

Excitement and fear is a hindrance.I think it comes from being afraid of the unknown.I suggest reading the suttas or learning the proper meditation techniques so you develop confidence or faith in the practice.

I have heard that meditation can be harmful- is this a sign that I should refrain from meditating?

I don't think meditation is harmful.i think our minds are harmful.Meditation is only a tool to clear away the things we store in our minds,to make conscious the subconscious.

What you experience during your practice is absolutely not harmful. It is a stage in the meditation process. More: it is a sign that you proceed in the right direction.

The vibrating 'light' that arises and passes away is the so-called nimitta.

Catherine, Shaila, (2008) Focused and Fearless. A Meditator’s Guide to States of Deep Joy, Calm, and Clarity p. 116:

‘The breath nimitta usually appears as a stable, smooth, white radiance associated with the focus on the breath. It is a mental reflection of the breath and includes no physical aspect; the light and breath may appear to have merged into a single mental experience of breath.’

Dalai Lama & Chodron, Thubten, (2014), Buddhism. One Teacher, Many Traditions p. 88:

‘The learning sign [nimitta] is an image arisen from this physical sensation [the sensation of the breath at the nostrils and upper lip, as it enters and exits]. When it arises, the meditator turns her attention to the nimitta—a colored luminous sphere or a radiant light—and that becomes his object of meditation [i.c. the arising and passing away of this nimitta].’

Brahm, Ajahn, (2011) The Art of Disappearing. The Buddha’s Path to Lasting Joy p. 120-121:

‘If you haven’t experienced these things, it can all sound like fantasy. But as your meditation improves, you gradually start to realize that this is not fantasy, that these states do exist, and what I’m saying is valid.

All you need to do is take your meditation further and drop more of the body. As you practice in this way, you start to bliss out. You understand that the body isn’t just suffering because of old age, sickness and death, but even its normal state is a huge heap of suffering. This is one of the incredible powerful realizations you get from deep meditation. A nimitta is enough to give you this realization, but if you get into jhana it’s unmistakably clear.’

When in meditation, you will pass through different psychic experiences. Here are some points:

• I would suggest trying meditating on a chair so that your feet are on the ground. If you feel panic or excitement rising, feel the soles of your feet. This will help you get grounded.
• Feel the sensation on different parts of your body. Learn to rest in the sensation of your body.
• You might try to combine meditation with a physical excercise (qigong, jogging, you name it)
• Don't get excited by psychic experiences. Panic and extreme excitement are the different sides of the same coin. Never search for psychic experiences.
• Remember you are free at any time to open your eyes and look around to make sure you are safe and not under any physical threat.
• I wouldn't watch horror movies or do other things that flirt with the fear in the psyche.
• If the panic strikes, endeavour to get back in the stillness of your own sensation. Remember that these energies are all appearances. They are not real in a physical sense so they cannot really harm you.