I'm scared!

I was surfing the net and felt hungry. I went downstairs to make myself an oat drink. When I came up, I saw this little creature (lizard) that I’m afraid the most. How did this fella entered my room. I sitting here wide awake figuring out how to chase him away. I can't see him anymore. He’s hiding behind my air cond. Now I'll never fall asleep. I hope he finds his way outside soon. Each time I see a lizard in a room, I do not dare to sleep in my room. I’ll pack my pillow & blanket & sleep in the living room. I’ll be doing that now. Sigh

Can anyone tell me how to prevent it from entering the house?