Amateur Night actress and best-selling author Jenny Mollen has been plenty open with fans when it comes to her pregnancy 鈥 she and husband Jason Biggs announced they were expecting聽back in April with a joke about how they conceived and even live Instagrammed the birth of their son, Lazlo. Now, Mollen is taking to social media once more to share the major post-pregnancy health scare she鈥檚 been dealing with post-pregnancy.

Posting a photo of herself looking down at the sidewalk, the 38-year-old wrote, 鈥淢any of you have written and asked me about my rapid weight loss. Weight loss that to be honest, I couldn鈥檛 really explain until now. This morning I woke up with a giant bulge in my neck the size of a golf ball. I had blood work and an ultrasound and will be waiting for the results over the weekend. Though I am not certain, I have good reason to believe it is some sort of hyperthyroidism. Apparently this is common in women AFTER PREGNANCY,鈥

While she conceded there had yet to be a diagnosis, saying, 鈥淚 really don鈥檛 know what鈥檚 going on, I won鈥檛 know until Monday,鈥 she鈥檚 pretty sure she鈥檚 found her culprit. 鈥淚鈥檓 predicting that I have hyperthyroidsim,鈥 she shared in a subsequent Instagram story.

Hyperthyroidism occurs when your thyroid gland produces too much of the hormone thyroxine, which can, in turn, considerably speed up your metabolism and result in serious weight loss. A version of the condition known as postpartum thyroiditis occurs after pregnancy and sees the thyroid gland becoming inflamed for no apparent reason. Thankfully, it鈥檚 painless and thyroid function usually returns to normal within 12 to 18 months.

Still, it鈥檚 always a good idea to talk to your doctor if you experience any of its symptoms, including enlarged thyroid, anxiety, heart palpitations, unexplained weight loss, fatigue, increased sensitivity to heat, or insomnia.

Have you, or anyone you know, battled hyperthyroidism? Tweet us @BritandCo.

(Photos via Jemal Countess/Getty)