Lump on back of head, painless and no injury

[Flyingwithoutwings]

As the title really. Noticed it yesterday, it's about a cm in diameter. Not sure that it's fully circular.
So my history is that I have back trouble, am hyper mobile so my bones go in and out fairly frequently. I've had swelling in my neck (lumps to the sides) before. I am used to that.
Had back trouble this week, mid back was locked up, had treatment yesterday.

Lat night I was washing my hair and felt this lump. It's about 1cm up from the base of my skull and 1cm in from the middle bit (where the cervical spin is). I air on the side of caution with measurements as it actually feels about an inch in each direction but I know it's unlikely to be that much.

I have no other symptoms... Is a lump in this area normal? DH had a fell and a look and it's definitely not the same on the other side and it's not red / hot.

How long should I wait before getting it looked at?

Sorry for the spelling errors: my DS kept grabbing the phone

could it be one of THESE, a type of cyst known as a wen ?

Hmmm, possibly could be.
I'm taking lots of anti inflammatories at the moment due to back pain and AF (who arrived yesterday). I hoped it would have reduced in size now if it were related.
Think I'll give it a few more days and then pop to the GP.
Feel like a pillock going for a lump on my head, but I'm curious to know what it could be.
Had a cracking headache last night but AF often gives me one of those

Most likely a sebaceous cyst (aka a wen as Hazel says). This a very common place for them. As with all new lumps, get your GP to check it if it doesn't disappear in a week or so but don't worry.

Thanks. I'm not too worried and wouldn't rush to GP. Whilst AF is here I tend to put everything down to that!!
Will leave it until the end of the week, just realised I have an osteopath appointment on Fri so I can ask if it's back-pain related.

Thanks for the suggestions

Are you sure it's not a lymph node? There are some just above the base of the skull, on both sides (but only one might have swollen up)?

Honestly don't know. It's hard and immobile. Will heck with osteopath on Fri and see GP next week if it's not related to my back problems.
It hasn't gone down though

I've got quite a few, had them for years. gp said they were cysts.