There is no single cause for all your symptoms. I will take them sequentially 1 floaters and flashes. To tell you 'not to worry' you need to be seen by an Eye MD that specializes in retina, vitreous and macular surgery. Among the tests you need are dilated exam with scleral depression of peripheral retina, macular OCT, perhaps fluorscene angigraphy. After this is done if new floaters, flashes, loss or peripheral vision occurs you need to see the retina specialist immediately. The flashes of light with a retina tear or posterior vitreous detachment (PVD) are momentary. If your flashes persist to 5-30 minutes are are constant like a neon sign that is not what retina flashes look like which are momentary, very short duration. 2. your eye being irritated. This is not due to PVD and may be some minor extermal problem, an external exam by a general ophthalmologist should find the cause quickly. 3. Visual strobing and headache. If these reoccur you will need to see an ophthalmologist and perhaps a neurologist. So not a single cause. Your final questions a constant spot in the peripheral vision can be due to vascular problems in the eye, fluid under the retina. Tell the retina surgeon about it. A visual field, peripheral vision test would be indicated also.