CAN I GAIN IT ALL BACK IN ONE DAY?

Hello, this sounds stupid but - i ve been living healthy and exercising and even though i eat enough , i lost quite a bit of weight in past week (the first week of my healthy lifestyle). However, today I got out of my regime and ate everything i could find. i even ordered pizza and ate it all, i ate chocolate and ice cream and stuff like that. I feel horrible now and the worst thing i am scared of is that i am going to wake up tomorrow morning and have all that weight that i lost during past week -its not too much but i can see it- back. I am terrified and i dont know what to do, like if i should start throwing up or use laxatives or something like that. I am going for a run tonight as soon as my stomach settles down. somebody please help!!!!!