Declaring

For reference, I had my first ever job interview the other day and it just sank in that I forgot to declare my disability. I'm UK based for reference. So, my disabilities in themselves do not inhibit my ability to work in any way or really require any extra adjustments. All I need are access to a bathroom every 3 hours or so during a shift. My shifts are 4 hours long for the first while, then it'll increase to 8 hours. Was the failure to mention it detrimental? Will I get into trouble for bringing it up after i get hired? I do have a medical alert necklace with an emergency number just in case if that helps.