You may not be imagining it. There is a thing called methotrexate pneumonitis - inflammation of the lungs:
* Methotrexate pneumonitis is an unpredictable and life-threatening side effect of methotrexate therapy.
* Presentation is often subacute with symptoms often present for several weeks or months before diagnosis.
* Presents most often with cough, dyspnoea and fever. May progress rapidly to respiratory failure.
* Early diagnosis, cessation of methotrexate, and treatment with corticosteroids and/or cyclophosphamide are important in management.
* There is a high rate of recurrence of lung injury after re-challenge with methotrexate.
I stopped it because of giving me serious lung/chest pain, and completely wiping me out for two days following the dose.
If in doubt got to your doc.
Beth